[ATO-1652] Add target to check if gRPC code is in sync with generated python code

[radovanZRasa]

Add Makefile target to check if gRPC .proto files and generated Python code are in sync. Target is part of existing make lint which is already part of CI.

Status (please check what you already did):

• [ ] made PR ready for code review
• [ ] added some tests for the functionality
• [ ] updated the documentation in the rasaHQ/rasa
• [ ] updated the changelog (please check changelog for instructions)
• [ ] reformat files using black (please check Readme for instructions)