Port of force-post-migration-dir-schema-load to EE

What does this MR do?

EE port of https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/21689

Ensure the schema is loaded with post_migrations included

If doing a schema load, the post_migrations should also be marked as up, even if SKIP_POST_DEPLOYMENT_MIGRATIONS was set, otherwise future migration runs will be broken.

This is helpful for the installation management scripts like our own takeoff script, or the cloud native charts, as they set the variable without actually knowing if the database is being seeded or migrated.

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/distribution/gitlab-operator/issues/27

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• EE specific content should be in the top level /ee folder
• For a paid feature, have we considered GitLab.com plans, how it works for groups, and is there a design for promoting it to users who aren't on the correct plan?