Made it possible to add annotations to the job itself.

What does this MR do?

We need to be able to set annotations on jobs in our Gitlab deployment, so here's an option to allow setting gitlab.migrations.job.annotations in the helm chart.

Specifically we want to use Argo CD to manage the Gitlab deployment and it defaults to sync'ing the job after the deployments have finished upgrading, which leads to a deadlock when migrations are needed.

Test plan indicating conditions for success has been posted and passes

Set gitlab.migrations.job.annotations and use helm template to see that the migrations job now contains the expected annotations.

Documentation created/updated

This works exactly like the existing gitlab.migrations.annotations, though I can not find any documentation for that either, so it's hard to know where to put the documentation, for the most part the helm chart seems to serve as the only documentation.