Store merge request diffs externally when outdated
A bucket for external diffs is specified in GET, but the functionality wasn't enabled. The MR enables external diffs to store outdated merge request diffs externally in object storage, while keeping current diffs in the database.
More details in https://docs.gitlab.com/ee/administration/merge_request_diffs.html#alternative-in-database-storage.
Edited by Nailia Iskhakova