Enable offloading old merge request diffs to object storage

In gitlab-org/gitlab-foss!25432 (merged) we implemented the offloading of merge request diffs to object storage. But it's a feature that needs to be enabled, see: https://docs.gitlab.com/ce/administration/merge_request_diffs.html#using-external-storage

Can we please enable this to remove literally terabytes of database records?

See recent evaluations of the impact of this table on our database: https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/8843#note_267877325