Collaborative locking

[juliusknorr]

Fixes #51 Fixes #57 Fixes #44

• [x] Extend lock to cover a collaborative lock for apps
• [x] Allow to extend lock TTL
• [x] Implement LockProvider as introduced in the OCP API
  • [x] Requires https://github.com/nextcloud/server/pull/31676
• [x] WebDAV based API for user locks, actual WebDAV standard locking is something for a follow up
• [x] API documentation https://github.com/nextcloud/files_lock/blob/enh/collaborative-lock/README.md#api
• [x] Basic feature tests for lock/unlock by users/apps
• [x] Update and propagate Etag on lock/unlock
  • [ ] Only the parent etags should be updated, however this currently does not seem to propagate then to the parents of an incoming file share for the recipient Would require https://github.com/nextcloud/server/issues/8477
• [x] Also add 412/423 status to OCS API
• [x] Expose meaningful message on 412/423 responses

This will enable the clients to already start with their implementation of file locking.

[solracsf]

Great work here! Thanks. 👏