Define sharding key for p_ci_pipeline_artifact_states for Geo verification state migration

Summary

Define and implement a sharding key for the p_ci_pipeline_artifact_states table to enable 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 defining sharding keys on tables that don't have them yet.

Current Status

Step	Status
Sharding Key Defined	⬜ Not defined
Backfill	⬜ Pending
Finalize	⬜ Pending
NOT NULL Constraint	⬜ Pending

Tasks

• Identify the appropriate sharding key (likely project_id based on parent table)
• Add sharding key column to the table
• Create backfill migration
• Run backfill on GitLab.com
• Finalize the backfill
• Add NOT NULL constraint
• Update table schema classification to gitlab_main_org
• Verify the table is included in organization migration replication

References

• Parent Epic: &20487 (closed)
• Table Schema: https://gitlab.com/gitlab-org/gitlab/-/blob/master/db/docs/p_ci_pipeline_artifact_states.yml