Allow renaming storage item prefixes (#9016)

* Implement parsing for #[pallet::storage_name] on storage items

* Rename storage prefix when a #[pallet::storage_name] is supplied

* Fix test_storage_info

* Rename storage_name to storage_prefix

* Check for duplicates when renaming storage prefixes

* Allow only string literals for storage_prefix renames

* Use proper spans for attribute errors

* Check for valid identifiers when parsing storage prefix renames