Add NOT NULL constraint to dependency_proxy_blob_states.group_id for Geo verification state migration

Summary

Add the NOT NULL constraint to the group_id sharding key column in the dependency_proxy_blob_states table to complete the migration strategy for Geo verification state tables.

Background

As part of the Geo verification state tables migration strategy for Protocell organization moves, we need to mark Geo verification state tables as gitlab_main_org instead of gitlab_main_cell_local/gitlab_ci_cell_local. This requires completing the sharding key work on these tables.

Current Status

Step	Status
Sharding Key Defined	✅ group_id
Backfill	✅ Complete
Finalize	✅ Complete
NOT NULL Constraint	⬜ Pending

Sharding Key Issue: #550700 (closed)

Tasks

• Add NOT NULL constraint
• Update table schema classification to gitlab_main_org in the db/docs YML file.
• Add the sharding_key attribute in the db/docs YML file.

References

• Sharding Guidelines: https://docs.gitlab.com/development/organization/sharding
• Parent Epic: &20487
• Table Schema: https://gitlab.com/gitlab-org/gitlab/-/blob/master/db/docs/dependency_proxy_blob_states.yml
• Backfill MR: !169237 (merged)
• Finalize MR: !185870 (merged)