[Audit Events] Asynchronous database index addition

What does this MR do and why?

This commit is step 1 to to add a migration to create the index_audit_events_on_entity_id_and_entity_type_and_created_at database index asynchronously on GitLab.com.

The synchronous index will be added in the followup #411129 (closed)

related to #337757 (closed)

resolves: #411167 (closed)

Changelog: added

EE: true

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