Specify a retention period for audit events

Problem to solve

We should plan to retain audit data indefinitely, but some instances may need to specify a retention period for retaining data (I want to keep data for X years) or removing it (I want to remove data older than Y years).

Proposal

Prune worker for audit_events with the ability for an admin to set a configurable period in the admin panel.

Lots of warnings when this will result in the removal of data (e.g. admin is trying to set a retention period that would result in the worker immediately removing data).

Links / references