Implement `check_uniqueness` management command
Checks that database is ready for UniqueConstaints. If an offending entity is found ask if you want to remove it.
Accepts two options:
--yes
- instatly remove entities without asking.
--dry-run
- only print the entities.
This patch is a part of upstream MR: https://gitlab.com/lava/lava/-/merge_requests/2235
Once the instance is free of uniqueness violations, rest of the upstream MR (including database migrations) will be imported.