Add class SnippetRepositoryStorageMove

What does this MR do?

This MR just adds the SnippetRepositoryStorageMove class to store repository storage moves for snippets. All the necessary logic has already been merged or going to in follow-up MRs.

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 #218992 (closed)