Add services to create abuse report notes

What does this MR do and why?

It adds services to create a new abuse report note.

Follow-up issues were created and linked as todos in the service comments.

Screenshots or screen recordings

How to set up and validate locally

This does not change the functionality, only prepares services. The endpoints will come in the follow-up MR, task: https://gitlab.com/gitlab-org/gitlab/-/issues/458264?work_item_iid=477331