Deprecate local param in get_mapping.json (#57265)

Relates: #55014

This commit deprecates the local param in get_mapping.json.
This parameter is a no-op and field mappings are always retrieved locally.

(cherry picked from commit 0b041cc)

Author: russcam

rest-api-spec/src/main/resources/rest-api-spec/api/indices.get_mapping.json

@@ -96,7 +96,11 @@
       },
       "local":{
         "type":"boolean",
-        "description":"Return local information, do not retrieve the state from master node (default: false)"
+        "description":"Return local information, do not retrieve the state from master node (default: false)",
+        "deprecated":{
+          "version":"7.8.0",
+          "description":"This parameter is a no-op and field mappings are always retrieved locally."
+        }
       }
     }
   }