Finalize setting sharding key for abuse_report_events

Everyone can contribute. Help move this issue forward while earning points, leveling up and collecting rewards.

• Collaborate/take over this issue

n #553429 (closed) we:

• added organization_id column to abuse_report_events table
• started populating the column, including validation on create
• set desired_sharding_key so that the values are backfilled

After the data are backfilled, we have to:

• set sharding_key
• set organization_id presence validation not only on create but also update
• set not null constraints on the column