Add deprecation status for Ai events.

Summary

Several AI events already deprecated, which means that old data should stay but no new events should be added. Current AI framework allows to add new events with unused event type and we need to fix that.

Proposal

Add deprecation status to AI event definition which should:

• Prevent new events from saving
• Still allow to read old events with deprecated type from DB.
• Adjust GraphQL type to mention deprecation status.