Hi there

This PR continues the work from #507. I've made a mistake and closed the PR by accident.

In #505 I've talked about testing the docker integration of the symfony cli more sophisticated. I've implement a proposal which includes testcontainers which start specific containers and checks if the symfony cli generates the correct variables.
The downside of this approach is that the developer which runs tests should have a docker host available (either local installed or configured with the env variable DOCKER_HOST).
Also I'm quit unsure if the tests should be refactored. This is due the fact that I haven't a lot of experience in Go, so perhaps someone can look into it and guide me in the right direction, if the tests are ok.
Thanks!

I've reworked the testcontainers integration by providing docker-compose files for each scenario. It should help maintaining and debugging this test.

Thanks for looking into it. Feedback is very welcome!