fix backwards compat for envoy command

The compatv2 integration tests were failing because they use an older CLI version with a newer
HTTP API. This commit restores the GRPCPort field to the DebugConfig output to allow older
CIs to continue to fetch the port.

.changelog/10588.txt

@@ -0,0 +1,4 @@
+```release-note:deprecation
+config: the `ports.grpc` and `addresses.grpc` configuration settings have been renamed to `ports.xds` and `addresses.xds` to better match their function.
+```
+

agent/agent_endpoint.go

@@ -93,9 +93,14 @@ func (s *HTTPHandlers) AgentSelf(resp http.ResponseWriter, req *http.Request) (i
 		Server:            s.agent.config.ServerMode,
 		Version:           s.agent.config.Version,
 	}
+	debugConfig := s.agent.config.Sanitized()
+	// Backwards compat for the envoy command. Never use DebugConfig for
+	// programmatic access to data.
+	debugConfig["GRPCPort"] = s.agent.config.XDSPort
+
 	return Self{
 		Config:      config,
-		DebugConfig: s.agent.config.Sanitized(),
+		DebugConfig: debugConfig,
 		Coord:       cs[s.agent.config.SegmentName],
 		Member:      s.agent.LocalMember(),
 		Stats:       s.agent.Stats(),