[ATO-2731] Initialise gRPC health check service

[radovanZRasa]

Makefile

Added new target in Makefile which will build docker image with dev dependencies.

Initialise gRPC health check service

Health check for gRPC server is initialised. Added Integration tests for gRPC server:

• when run in standalone mode - target to run tests is added to Makefile
• when run as docker container - targets to setup env and run tests are added to Makefile Added CI steps which will run integration tests, using targets from Makefile.

Generate SSL certificates

Added Makefile with targets to generate SSL certificates, located under certs directory. Generated certificates will be placed in certs directory because that will prevent accidental commit of the certificates (see cert/.gitignore). Move generated certificates and keys you need, to the directory of integration test for which they will be used.

Status (please check what you already did):

• [x] made PR ready for code review
• [x] 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)