Add deploy token handling in audit event generation

What does this MR do and why?

Now that we are streaming git events, we want to handle deploy token as author for audit events.

How to set up and validate locally

1. Enable the feature flag audit_event_streaming_git_operations on the instance in question.
2. Create a private project on a group with an Ultimate licence.
3. Create a deploy token, with read_repository, scope for the project. (Settings -> Repository -> Deploy tokens)
4. Clone the repository using http credentials.
5. Use the deploy token user/password as the credentials.
6. Check audit event is streamed and git clone is successful.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #359066 (closed)