Move GitHooksService into Gitlab::Git

What does this MR do?

• move GitHooksService in to Gitlab::Git
• decouple GitHooksService from User and Project
• make gl_repository an attribute of Gitlab::Git::Repository

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

We want to move the code that creates commits and updates refs in repositories into Gitlab::Git.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?