Draft: Added audit event for tracking bot user deletion

What does this MR do and why?

Solves #488166 (closed)

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

How to set up and validate locally

1. Create a Group Access Token https://docs.gitlab.com/ee/user/group/settings/group_access_tokens.html#use-the-ui
2. Revoke Token using the revoke button on the token table
3. Observe a new audit event added to Group Audit Events