fix(federation): Fix missing protocol on CloudID remote

[nickvergessen]

Seems that some paths inside the external storage logic don't contain the protocol. Since it's too hard to track down within the full code base, it's easier to simply enforce the protocol within the cloud ID manager.
I had ended up with:

 Undefined array key 1 at apps/files_sharing/lib/External/Cache.php#25

server/apps/files_sharing/lib/External/Cache.php

Line 25 in 1e04619

[, $remote] = explode('://', $cloudId->getRemote(), 2);

• Follow up to fix(federation): ICloudId->getRemote() should contain the protocol #44625

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[nickvergessen]

/backport to stable29

[ArtificialOwl]

faced the issue while working on https://github.com/nextcloud/server/pull/45979/files#diff-70371b3022845d468bcd2be6a3dd06d5ffe655f958f1b737bb5a107a206e3f2c
quickly fixed on my side but i guess it is now useless :)