Switch to using dynamic child pipelines

Use dynamic child pipelines feature to generate QA jobs depending on if the job would run any tests.

Related to: https://gitlab.com/gitlab-org/quality/team-tasks/-/issues/564

Notes for the reviewer:

1. There is a bug that limits the number of dotenv variables to 20. We are requesting to prioritise fixing the bug but until then, we have a capacity of 5 more variables before we reach the limit.
2. There is another bug with the the dotenv variables where the rules in the child pipeline cannot access the vars. This MR currently uses a work around proposed by Marius but that means setting the variables twice.