[WebDAV] Implement command pattern, streamline lifecycle, remove WebdavScope (#1617)

* Remove WebdavScope as it is no longer needed

* [WIP] DavDocumentsProviderImpl

* [WIP] Move DavDocumentsProvider to BaseDavDocumentsProvider and implementation to DavDocumentsProvider

* Adapt tests and DI

* [WIP] Implement Command pattern

* Finish Command pattern, add deprecation notices

* Unify DavDocumentsProvider with wrapper again

* Get rid of DavDocumentsActor

* Add notes about lifecycle, remove shutdown