Add MeshExtension API to extensions

extensions/v1alpha1/wasm.proto

@@ -356,6 +356,9 @@ message WasmPlugin {
   // More details can be found [here](https://www.envoyproxy.io/docs/envoy/latest/api-v3/extensions/wasm/v3/wasm.proto#extensions-wasm-v3-vmconfig).
   VmConfig vm_config = 11;
 
+  /* NOTE: This nested type is intentionally kept for backward compatibility.
+     The canonical definition is the top-level TrafficSelector in
+     extension_filter.proto. */
   // TrafficSelector provides a mechanism to select a specific traffic flow
   // for which this Wasm Plugin will be enabled.
   // When all the sub conditions in the TrafficSelector are satisfied, the
@@ -414,6 +417,8 @@ enum PluginType {
   NETWORK = 2;
 }
 
+/* NOTE: This enum is intentionally kept for backward compatibility with WasmPlugin.
+   The canonical definition is ExecutionPhase in traffic_extension.proto. */
 // The phase in the filter chain where the plugin will be injected.
 enum PluginPhase {
   // Control plane decides where to insert the plugin. This will generally