Fixes#7110
This PR declares docker-compose as a requirement for certbot-ci. This way, a recent version of docker-compose is installed in the standard virtual environment set up by `tools/venv.py` and `tools/venv3.py`, and so is available to pytest integration tests from `tox` or in the virtual environment enabled.
* Add docker-compose as a dev dependency and declares it in certbot-ci requirements
* Update docker-compose 1.25.0