Allow collaboratively work on locked file

[tobiasKaminsky]

• share a file to user "test"
• work on this file online (e.g. via text, OO, Collabora)
• as user test
  • see that file is locked
  • after click on it: get offer to work collaboratively on it

[juliusknorr]

Things to expose from the DAV perspective:

• expose that the file is locked as an app with the app id
• app id should probably match with what is used through the direct editing API so that the right editor can be picked if needed

[juliusknorr]

Copying over notes from #45 to avoid having multiple issues about the same topic:

For collaborative editing with Text, Nextcloud Office or ONLYOFFICE it would be useful if the collaborative editing app could lock a file on behalf of the editing session rather than per-user based. This way sync clients and the web UI could indicate the file lock while the app itself which handles changes can properly write to it.

The basic idea would be that the app can issue a lock/unlock through some kind of exposed API, similar to the user one in https://github.com/nextcloud/files_lock/blob/master/lib/Service/LockService.php#L237

Then when performing write actions the app would need to have a method to exclude further detection of locks for operation, so that any follow up filesystem actions would not trigger the locking in https://github.com/nextcloud/files_lock/blob/master/lib/Storage/LockWrapper.php#L110

From the app perspective I imagine something like this:

public function openFile($fileId) {
    $this->lockService->lockFileForApp($fileId, 'text');
}

public function writeFile($content) {
    $this->lockService->enableAppScope('text');
    $file->putContents($content); // does not throw a LockedException if the lock is owned by the same app id
}

public function closeFile($fileId) {
    $this->lockService->unlockFileForApp($fileId, 'text');
}