feat(RichObjectStrings): Add missing Talk 'file' metadata fields

[provokateurin]

Summary

Clients should be able to rely on these fields, thus they should be documented in the definitions. These fields were added in nextcloud/spreed#7776 and nextcloud/spreed#11093.

I don't think backporting these changes is useful as this is only for documentation and validation purposes and doesn't fix any bug. For now I've set the since to the Server versions for the corresponding Talk releases, but it might make sense to set them only to 30.0.0 to avoid any confusion and instability.

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)