Add an option to disable whiteboards #104
Description
Since there is a "native" whiteboard app for Nextcloud (https://nextcloud.com/blog/nextcloud-whiteboard/) with its own backend, it may be helpful to disable the whiteboard feature in Draw.io, so there is no confusion which whiteboard app to use.
The preferrable solution would be an option in the administrative app settings to enable or disable the whiteboard integration. If the whiteboard integration is disabled, the "New draw.io Whiteboard" in the files app would be removed, so people do not create "wrong" whiteboard files by accident.