feat: add LUA script Envoy extension support for API gateway

[Vikramarjuna]

Description

Extended LUA Script Envoy extension support for API Gateway

Testing & Reproduction steps

1. Create a cluster with API gateway
2. Inject LUA script to API gateway using either service defaults or proxy defaults. Sample script:

{
    name     = "builtin/lua"
    required = true
    arguments = {
      proxyType = "api-gateway"
      listener  = "outbound"
      script    = <<EOT
        function envoy_on_response(response_handle)
          if response_handle:headers():get(":status") == "404" then
              response_handle:headers():replace(":status", "200")
              local json = '{"message":"Modified by Lua script","status":"success"}'
              response_handle:body():setBytes(json)

              response_handle:headers():remove("x-envoy-upstream-service-time")
              response_handle:headers():remove("x-powered-by")
              response_handle:headers():replace("cache-control", "no-store")
              response_handle:headers():remove("content-length")
              response_handle:headers():replace("content-encoding", "identity")
              response_handle:headers():replace("content-type", "application/json")
          end
        end
      EOT
    }
  }

3. Request a non-existent page and see that the response is as provided in the LUA script and headers are modified as per the script.

Links

https://hashicorp.atlassian.net/browse/NET-12465

PR Checklist

• updated test coverage
• external facing docs updated
• appropriate backport labels added
• not a security concern

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