Operator does not create non default service accounts

In the situation where you do not specify a serviceaccount or set it to gitlab-runner-sa, the Operator will create this SA for you.

If you pick any other name for the serviceaccount, the operator will not create a SA. This means you need to create the SA manually, and ensure the gitlab-app-role is bound to the custom service account else it will not function.

This feels unintended and requires careful sequencing of commands. Create SA, apply gitlab runner CRD, attach role binding.

The operator should have logic to check if the SA being referenced already exists, if it does, just 'pick it up' like the current behaviour is as you can assume the user has intentionally created and customised one. If the custom SA does NOT exist, the operator should create it.