Clean up schema for table protected_tag_create_access_levels
Per https://gitlab.com/gitlab-com/infrastructure/issues/1709 (private to GitLab employees):
- Wrong data type: created_at should be timestamptz
- Wrong data type: updated_at should be timestamptz
- Missing constraint: UNIQUE (protected_tag_id)
Unused columns (?):
- user_id is always NULL
- group_id is always NULL
These columns may be NULL because nobody on GitLab.com uses them. If they are not used by the application at all we can remove them.
Edited by Yorick Peterse