Add sharding keys for vulnerability_management

Add sharding keys for feature category vulnerability_management.

These tables have been identified as cell local tables.

All cell local tables require a sharding key.

A sharding key has been automatically selected for these tables. The sharding key was chosen because it is a NOT NULL column referencing either projects or namespaces.

Additionally, gitlab_schema has been set to gitlab_main_cell for any tables didn't use this schema already. For these tables we have also added allow_cross_joins, allow_cross_transactions and allow_cross_foreign_keys. These will silence any existing violations, allowing the pipeline to pass without requiring further changes. In the future, we'll remove these allow_... statements and fix any violations as they arise. You can read more about this in the documentation for multiple databases

We have assigned a random backend engineer from groupthreat insights to review these changes. Please confirm that each table should indeed be cell local, and that the selected column is an appropriate sharding key. When you are finished, please request a review from the database maintainer suggested by Danger.

If you have any questions or concerns, reach out to @tigerwnz or @DylanGriffith.

This change was generated by gitlab-housekeeper