Add and backfill project_id for deployment_clusters

What does this MR do and why?

Add and backfill project_id for deployment_clusters.

This table has a desired sharding key configured (view configuration).

This merge request is the first step towards transforming the desired sharding key into a sharding key.

This involves three changes:

• Adding a new column that will serve as the sharding key (along with the relevant index and foreign key).
• Populating the sharding key when new records are created by adding a database function and trigger.
• Scheduling a batched background migration to set the sharding key for existing records.

Once the background migration has completed, a second merge request will be created to finalize the background migration and add a not null constraint.

#583002