tcp: add FilterState hash policy for TcpProxy and other network filters (#18701)

Adds a new variant to type.v3.HashPolicy to generate a hash from an object in FilterState. This implementation mirrors what already exists for HTTP filters (see RouteAction.HashPolicy.FilterState), and is usable by network filters such as TcpProxy.

Risk Level: low
Testing: updated tests in tcp_proxy:config_test
Docs Changes: N/A
Release Notes: added an entry under tcp
Platform Specific Features: N/A

Signed-off-by: Dan Rosen <mergeconflict@google.com>

Mirrored from https://github.com/envoyproxy/envoy @ 38739c32b39da483782fa18dc5a5aa77cee677ab

envoy/api/v2/route/route_components.proto

@@ -675,8 +675,8 @@ message RouteAction {
 
     message FilterState {
       // The name of the Object in the per-request filterState, which is an
-      // Envoy::Http::Hashable object. If there is no data associated with the key,
-      // or the stored object is not Envoy::Http::Hashable, no hash will be produced.
+      // Envoy::Hashable object. If there is no data associated with the key,
+      // or the stored object is not Envoy::Hashable, no hash will be produced.
       string key = 1 [(validate.rules).string = {min_bytes: 1}];
     }
 

envoy/config/route/v3/route_components.proto

@@ -752,8 +752,8 @@ message RouteAction {
           "envoy.api.v2.route.RouteAction.HashPolicy.FilterState";
 
       // The name of the Object in the per-request filterState, which is an
-      // Envoy::Http::Hashable object. If there is no data associated with the key,
-      // or the stored object is not Envoy::Http::Hashable, no hash will be produced.
+      // Envoy::Hashable object. If there is no data associated with the key,
+      // or the stored object is not Envoy::Hashable, no hash will be produced.
       string key = 1 [(validate.rules).string = {min_len: 1}];
     }
 

envoy/type/v3/hash_policy.proto

@@ -23,9 +23,20 @@ message HashPolicy {
     option (udpa.annotations.versioning).previous_message_type = "envoy.type.HashPolicy.SourceIp";
   }
 
+  // An Object in the :ref:`filterState <arch_overview_data_sharing_between_filters>` will be used
+  // to compute the hash used by hash-based load balancing algorithms.
+  message FilterState {
+    // The name of the Object in the filterState, which is an Envoy::Hashable object. If there is no
+    // data associated with the key, or the stored object is not Envoy::Hashable, no hash will be
+    // produced.
+    string key = 1 [(validate.rules).string = {min_len: 1}];
+  }
+
   oneof policy_specifier {
     option (validate.required) = true;
 
     SourceIp source_ip = 1;
+
+    FilterState filter_state = 2;
   }
 }