Test that services feature functions as expected

In containerized environments, we allow defining a service that can be launched as a side-car container and used in conjunction with the main job. Typical usecases are for databases like mysql, postgresql, or redis. Docs are here https://docs.gitlab.com/ee/ci/services/

We should test that the services keyword and related feature (name, alias, etc) work. We don't need to do an exhaustive check against all popular ones because we want to focus on testing our code and not, for example, mysql's latest container build (we might want to also check that, but likely in a different test environment).

@steveazz has a good sample snippet of a scenario that tests a postgres service here https://gitlab.com/steveazz/playground/-/blob/service/.gitlab-ci.yml