Call RenameRepository instead of RenameNamespace

What does this MR do?

This MR changes LegacyNamespace so that on a rename it moves legacy repositories over to hashed storage.

It also changes the way that gitlab_shell moves repositories. Instead of renaming the whole namespace, it now calls a new RPC we have on Gitaly RenameNamespace

This will need gitaly!1471 (merged) to be merged and tagged in a new gitaly version first

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry for user-facing changes, or community contribution. Check the link for other scenarios.
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team