feat: Implement handling for lock managers who can unlock files

[juliusknorr]

Fixes #52

• Allow unlock for
  • The file owner
  • Users who have permissions to manage ACL on groupfolders
    • Needs upstream fix and testing as groupfolders on master branch currently does not fetch the webdav properties
  • A allow list for a dedicated group of users who are considered to be allowed to manually remove a lock
    • Needs a UI to set this

[Jerome-Herbinet]

Hi @juliushaertl,
Will your PR :

• give more rights to unlock files to the mentioned users
• add an admin page (in settings) to list locked files, with an unlock button for each remaining locked file
  Thanks by advance

[Mika-6-9]

Hi.
Very very good idea, if possible see and take into account the synchronization client (Nextcloud Desktop https://github.com/nextcloud/desktop) which automatically locks and unlocks Office files (Word/Excel/Powerpoint)
Thanks

[Mika-6-9]

Hi
Do you have any idea when the rest of this PR will be implemented?
Now, the file owner can force the unlocking resulting from a client, when will the possibility for an admin or even better a delegation of power be available so that we can unlock for others?
Thanks