Adapt to new pattern of Migrations Job naming

Summary

gitlab-org/charts/gitlab!3602 (merged) updates the calculation of the Migrations Job name.

We currently do some light manipulation of this in controllers/gitlab/migrations.go, which includes giving it a hash as well as adding pre to the name for Jobs that only run pre-migrations.

Acceptance criteria

• When/if gitlab-org/charts/gitlab!3602 (merged) is merged, update the Operator codebase to reflect this new pattern