Add audit events for registry tag deletion

What does this MR do and why?

Creates the container_repository_tags_deleted audit event, to be logged whenever a project's container registry tags are marked for deletion through DeleteTagsService.

How to set up and validate locally

1. Create a project
2. Build and push a container image to the repository as described here.
3. Check Deploy > Container Registry for that project, and find the new repository (it may take a few minutes to appear).
4. View the repository's tags, then delete one or more via the icon.
5. Verify an audit event is created for the tag being deleted.

Related to #362290 (closed)