Add target to check if gRPC code is in sync with generated python code

Makefile

@@ -38,6 +38,7 @@ lint:
 	poetry run ruff check rasa_sdk tests --ignore D
 	poetry run black --exclude="rasa_sdk/grpc_py" --check rasa_sdk tests
 	make lint-docstrings
+	make check-generate-grpc-code-in-sync
 
  # Compare against `main` if no branch was provided
 BRANCH ?= main
@@ -69,3 +70,8 @@ generate-grpc:
 	 	--pyi_out=. \
 	 	proto/action_webhook.proto \
 	 	proto/health.proto
+
+check-generate-grpc-code-in-sync: generate-grpc
+	# this is a helper to check if the generated code is in sync with the proto files
+	# it's not run on CI at the moment
+	git diff --exit-code rasa_sdk/grpc_py | if [ "$$(wc -c)" -eq 0 ]; then echo "Generated code is in sync with proto files"; else echo "Generated code is not in sync with proto files"; exit 1; fi