tcp_proxy: add support for subset load balancing (#8870 An error occurred )

Add support for subset load balancing into tcp_proxy

Risk Level: Medium
Testing: unit tests, integration tests, manual testing
Docs Changes: docs/root/configuration/listeners/network_filters/tcp_proxy_filter.rst
Release Notes: docs/root/intro/version_history.rst
Fixes #8769
  
An error occurred
 


This PR adds support for metadata_match field per weighted cluster, e.g.

name: envoy.tcp_proxy
typedConfig:
  '@type': type.googleapis.com/envoy.config.filter.network.tcp_proxy.v2.TcpProxy
  statPrefix: postgres.internal:5432
  weighted_clusters:
    clusters:
    - name: postgres.internal:5432
      metadata_match:              # implemented by this PR
        filter_metadata:
          envoy.lb:
            role: master
      weight: 10
    - name: postgres.internal:5432
      metadata_match:              # implemented by this PR
        filter_metadata:
          envoy.lb:
            role: replica
      weight: 90

Signed-off-by: Yaroslav Skopets <y.skopets@gmail.com>

Mirrored from https://github.com/envoyproxy/envoy @ 5536ce73026fcbf1c176c09d409a981d67981047

envoy/config/filter/network/tcp_proxy/v2/tcp_proxy.proto

@@ -90,6 +90,14 @@ message TcpProxy {
       // determined by its weight. The sum of weights across all entries in the
       // clusters array determines the total weight.
       uint32 weight = 2 [(validate.rules).uint32 = {gte: 1}];
+
+      // Optional endpoint metadata match criteria used by the subset load balancer. Only endpoints
+      // in the upstream cluster with metadata matching what is set in this field will be considered
+      // for load balancing. Note that this will be merged with what's provided in
+      // :ref:`TcpProxy.metadata_match
+      // <envoy_api_field_config.filter.network.tcp_proxy.v2.TcpProxy.metadata_match>`, with values
+      // here taking precedence. The filter name should be specified as *envoy.lb*.
+      api.v2.core.Metadata metadata_match = 3;
     }
 
     // Specifies one or more upstream clusters associated with the route.

envoy/config/filter/network/tcp_proxy/v3alpha/tcp_proxy.proto

@@ -34,6 +34,14 @@ message TcpProxy {
       // determined by its weight. The sum of weights across all entries in the
       // clusters array determines the total weight.
       uint32 weight = 2 [(validate.rules).uint32 = {gte: 1}];
+
+      // Optional endpoint metadata match criteria used by the subset load balancer. Only endpoints
+      // in the upstream cluster with metadata matching what is set in this field will be considered
+      // for load balancing. Note that this will be merged with what's provided in
+      // :ref:`TcpProxy.metadata_match
+      // <envoy_api_field_config.filter.network.tcp_proxy.v3alpha.TcpProxy.metadata_match>`, with
+      // values here taking precedence. The filter name should be specified as *envoy.lb*.
+      api.v3alpha.core.Metadata metadata_match = 3;
     }
 
     // Specifies one or more upstream clusters associated with the route.