WIP: Backport API support to move between repository storages/shards

EE MR: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/15329

https://docs.gitlab.com/ee/development/ee_features.html#backporting-changes-from-ee-to-ce

What does this MR do?

Backport API support for admins to move projects between repository storages/shards using repository_storage attribute originally added in https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/533

Fix https://gitlab.com/gitlab-org/gitlab-ce/issues/50226

In support of https://gitlab.com/gitlab-org/gitlab-ce/issues/47599

Invalidates https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/31933

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