fix(metadata): Allow to load metadata of multiple files at once

[nickvergessen]

• Would be helpful for Talk to avoid a query per file: Add metadata to file parameters spreed#11093
• Similarly other apps like photos could benefit from it, but instead it currently uses exposure/manipulation via the query builder: https://github.com/nextcloud/photos/blob/aa82646be1493e74a00513757153e1759a8e3a69/lib/DB/Place/PlaceMapper.php#L59-L67

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 stable28

[tobiasKaminsky]

Is there any documentation for it?
I think this might be also useful for Files clients.

[nickvergessen]

I did not add an DAV/API endpoint.
That could/should be done by the initial feature developer if it's not there yet