Refactor repository move logic from the Project model into concern

What does this MR do?

Extracts some project logic related to repository moving into new RepositoryStorageMovable concern.

We're going to allow snippets to move the repository storage of their repositories (and later with group wikis). For this, we need to reuse some of the existent functionality in projects.

Therefore, the best way to do it is to extract it into a concern and include it in snippets. In issue #218987 (closed), we say that we should add this logic to the HasRepository concern but, until we add this logic to Group Wikis, we can't really move that logic there.

Does this MR meet the acceptance criteria?

Conformity

• [ ] Changelog entry
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Separation of EE specific content

Related to #218987 (closed)