Draft: Add qa-migration job

What does this MR do?

Adds a new job that will execute specs tagged :db_migrate. This is a reuse of specific tests that captured issues caused by DB migrations. It is to be executed within its own pipeline as an additional step after migrations are executed as part of the deployment to staging-canary.

Related to gitlab-org/quality/quality-engineering/team-tasks#1881 (closed)

Check-list

• Verify the change in all affected pipelines.