Adds fields to ProcessBundleRequest to prepare for future SDK skips for fetching/writing state.

Author: wolfchris-google

model/fn-execution/src/main/proto/org/apache/beam/model/fn_execution/v1/beam_fn_api.proto

@@ -415,6 +415,12 @@ message ProcessBundleRequest {
   // beam:protocol:control_request_elements_embedding:v1 capability. See more
   // at https://s.apache.org/beam-fn-api-control-data-embedding.
   Elements elements = 3;
+
+  // If "true", SDK will skip state fetch
+  bool key_has_no_state = 4;
+
+  // If "true", SDK will skip state write
+  bool only_bundle_for_key = 5;
 }
 
 message ProcessBundleResponse {