feat(ingress gateway): configure max_connections to upstream service

[huikang]

Description

As a user of ingress gateway, I want to increase the max_connections of the service in the ingress-gateway config entry (link to the detailed description). However, in current implementation, max_coonections can’t be changed and set to the default value of 1024 by envoy.

This PR adds a new field named MaxConnections to the service field of ingress-gateway config entry. The new field allows user to configure the max_connections of the upstream cluster of a specified service behind the ingress gateway.

• added unit test
• updated doc

Testing & Reproduction steps

Kind = "ingress-gateway"
Name = "my-ingress-gateway"

Listeners = [
 {
   Port = 8082
   Protocol = "http"
   Services = [
     {
        Name = "counting"
        Hosts = ["*"]
        MaxConnections = 5120          // <----- increase the max_connections
     },
     {
       Name = "counting-v2"
       Hosts = ["v2"]
     }
   ]
 }
]

• envoy cluster

counting.default.dc2.internal.ca9229ae-1b1d-af9d-47fa-43885f09557a.consul::default_priority::max_connections::5120
counting.default.dc2.internal.ca9229ae-1b1d-af9d-47fa-43885f09557a.consul::default_priority::max_pending_requests::1024
counting.default.dc2.internal.ca9229ae-1b1d-af9d-47fa-43885f09557a.consul::default_priority::max_requests::1024
counting.default.dc2.internal.ca9229ae-1b1d-af9d-47fa-43885f09557a.consul::default_priority::max_retries::3

Links

Address #13374

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PR Checklist

• updated test coverage
• external facing docs updated
• not a security concern

[kisunji]

This looks okay to me but will tag other members for review since I'm not too familiar with ingress gw code

[huikang]

Actually the else branch will never happen because

* The Proxy.Upstreams configuration is invalid for a ingress-gateway

Leave it here for safety check.

[boruszak]

I reviewed the docs in this PR, 14708.txt and ingress-gateway.mdx, only. I have one suggestion, but I was unsure of your intent. Please review my comment below, and let me know if you have any questions or need additional assistance.

Approving on behalf of consul-docs.

[huikang]

superseded by #14749