Clean up recorded webhook events

[AlexTugarev]

Followup to PR #11356

We should auto-delete recorded webhook events after a configured retain period.

[gtsiolis]

@AlexTugarev This is probably why prebuild events take 3 minutes to load for some high-activity projects, right? See relevant discussion (internal).

[AlexTugarev]

@gtsiolis, I ran the query for the mentioned project and it returned in a ~100ms, but in 1 out of 10 tries it was 3s. 🤷🏻‍♂️

[gtsiolis]

Oh, the page for the aforementioned project seems to load now in 1-3 seconds. 🤷