[THREESCALE-11701] Remove redis connection error message from response body in edge limiting policy

[tkan145]

What

Fix https://issues.redhat.com/browse/THREESCALE-11701

Close #1316

Verification steps

• Checkout this branch and build a new runtime-image

make runtime-image IMAGE_NAME=apicast-test

• Get into dev-environment

cd dev-environments/plain-http-upstream

• Edit apicast-config.json as follow

diff --git a/dev-environments/plain-http-upstream/apicast-config.json b/dev-environments/plain-http-upstream/apicast-config.json
index ff944273..b0193ee3 100644                                                                                                 
--- a/dev-environments/plain-http-upstream/apicast-config.json                                                                  
+++ b/dev-environments/plain-http-upstream/apicast-config.json                                                                  
@@ -13,6 +13,20 @@                                                                                                              
         "policy_chain": [                                                                                                      
           {                                                                                                                    
             "name": "apicast.policy.apicast"                                                                                   
+          },                                                                                                                   
+          {                                                                                                                    
+            "name" : "apicast.policy.rate_limit",                                                                              
+            "configuration" : {                                                                                                
+              "connection_limiters" : [                                                                                        
+                {                                                                                                              
+                  "key" : {"name" : "test3", "scope" : "global"},                                                              
+                  "conn" : 20,                                                                                                 
+                  "burst" : 10,                                                                                                
+                  "delay" : 0.5                                                                                                
+                }                                                                                                              
+              ],                                                                                                               
+              "redis_url" : "redis://invalidhost:1234/1"                                                                       
+            }                                                                                                                  
           }                                                                                                                    
         ],                                                                                                                     
         "proxy_rules": [                                                                                                                                                                                                                       

• Start gateway

make gateway IMAGE_NAME=apicast-test

• Send request

curl --resolve get.example.com:8080:127.0.0.1 -v "http://get.example.com:8080/?user_key=123"

• You should see 500 Internal Server Error

< HTTP/1.1 500 Internal Server Error                 
< Server: openresty                                  
< Date: Thu, 20 Feb 2025 01:58:19 GMT                
< Content-Type: text/html                            
< Content-Length: 174                                
< Connection: close                                  
<                                                    
<html>                                               
<head><title>500 Internal Server Error</title></head>
<body>                                               
<center><h1>500 Internal Server Error</h1></center>  
<hr><center>openresty</center>                       
</body>                                              
</html>                                              
* Closing connection                                 

• Now change the policy to log error instead

diff --git a/dev-environments/plain-http-upstream/apicast-config.json b/dev-environments/plain-http-upstream/apicast-config.json 
index ff944273..285ef37a 100644                                                                                                  
--- a/dev-environments/plain-http-upstream/apicast-config.json                                                                   
+++ b/dev-environments/plain-http-upstream/apicast-config.json                                                                   
@@ -13,6 +13,21 @@                                                                                                               
         "policy_chain": [                                                                                                       
           {                                                                                                                     
             "name": "apicast.policy.apicast"                                                                                    
+          },                                                                                                                    
+          {                                                                                                                     
+            "name" : "apicast.policy.rate_limit",                                                                               
+            "configuration" : {                                                                                                 
+              "connection_limiters" : [                                                                                         
+                {                                                                                                               
+                  "key" : {"name" : "test3", "scope" : "global"},                                                               
+                  "conn" : 20,                                                                                                  
+                  "burst" : 10,                                                                                                 
+                  "delay" : 0.5                                                                                                 
+                }                                                                                                               
+              ],                                                                                                                
+              "redis_url" : "redis://invalidhost:1234/1",                                                                       
+              "configuration_error": {"error_handling": "log"}                                                                  
+            }                                                                                                                   
           }                                                                                                                     
         ],                                                                                                                      
         "proxy_rules": [                                                                                                        

• You shall see 200 OK this time

< HTTP/1.1 200 OK                       
< Server: openresty                     
< Date: Thu, 20 Feb 2025 02:00:38 GMT   
< Content-Type: application/json        
< Content-Length: 294                   
< Connection: keep-alive                
<