thrift: configurable validate_clusters to override the default cluste… (#20874)

This is a continuation of #20577.

Additional Description:
Risk Level: low
Testing: unit test

Signed-off-by: kuochunghsu <kuochunghsu@pinterest.com>

Mirrored from https://github.com/envoyproxy/envoy @ 0be448e6d92dff8d609142a8e5492ebf03884779

envoy/extensions/filters/network/thrift_proxy/v3/route.proto

@@ -34,6 +34,21 @@ message RouteConfiguration {
   // The list of routes that will be matched, in order, against incoming requests. The first route
   // that matches will be used.
   repeated Route routes = 2;
+
+  // An optional boolean that specifies whether the clusters that the route
+  // table refers to will be validated by the cluster manager. If set to true
+  // and a route refers to a non-existent cluster, the route table will not
+  // load. If set to false and a route refers to a non-existent cluster, the
+  // route table will load and the router filter will return a INTERNAL_ERROR
+  // if the route is selected at runtime. This setting defaults to true if the route table
+  // is statically defined via the :ref:`route_config
+  // <envoy_v3_api_field_extensions.filters.network.thrift_proxy.v3.ThriftProxy.route_config>`
+  // option. This setting default to false if the route table is loaded dynamically via the
+  // :ref:`trds
+  // <envoy_v3_api_field_extensions.filters.network.thrift_proxy.v3.ThriftProxy.trds>`
+  // option. Users may wish to override the default behavior in certain cases (for example when
+  // using CDS with a static route table).
+  google.protobuf.BoolValue validate_clusters = 3;
 }
 
 message Route {