Goal: Set generic system password for Op -> Nextcloud. During save, username should always be "OpenProject" if storage provider type is nextcloud

* Begin of the insertion[x]End of the insertion Begin of the deletion [ ]End of the deletion Only show managed project folders form when there were no per-existing values (during edit of nextcloud)
* Begin of the insertion[x]End of the insertion Begin of the deletion [ ]End of the deletion Default values: toggle is on, require app password
* [ ] Validation of app password? - **Separate Implementation (WP)**. (E.g. query for an openproject folder/User)
* [ ] _There are validators for nextcloud - authentication via basic auth, user OpenProject. Username is saved in the database_