Event type information in protected branch audit event stream

What does this MR do and why?

Adds event type information in streaming audit event when we modify protected branch

How to set up and validate locally

1. Setup external destination using https://docs.gitlab.com/ee/administration/audit_event_streaming.html#use-the-gitlab-ui or https://docs.gitlab.com/ee/administration/audit_event_streaming.html#use-the-api .
2. Create protected branch https://docs.gitlab.com/ee/user/project/protected_branches.html#configure-a-protected-branch
3. Check audit event is created and streamed with correct event type. Also check audit event is visible at http://localhost:3000/admin/audit_logs and log is present in audit_json.log.
4. Modify protected branch
5. repeat step 3
6. Delete protected branch
7. repeat step 3

Action	Event typ
Create	protected_branch_created
Update	protected_branch_updated
Delete	protected_branch_removed

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 #363091 (closed)