Add QA specs for the new snippet repository storage move API

In &3393 (closed) we're making the necessary changes to introduce a new API that will allow us to move snippets' repository storage from one shard to another.

Once everything is implemented, it would be great to have QA specs to test it.

Projects, also have the same API, and we have QA specs to test it.

I've found so far in QA this class that can be easily reused for snippets.