Add GH actions with integration tests

[Alexander Emelin]

Start Centrifugo like this:

      - name: Start Centrifugo
        run: docker run -d -p 8000:8000 centrifugo/centrifugo:latest centrifugo --api_insecure

And run test suite: https://github.com/centrifugal/phpcent#testing

[Alexander Emelin]

Done