Enhancement: Implement historical way of constructing OCM WebDAV URL

Expose the expected WebDAV endpoint for OCM by OC10 and Nextcloud as described
in https://github.com/cs3org/OCM-API/issues/70#issuecomment-1538551138 to allow
reva providers to participate to mesh.

https://github.com/cs3org/reva/pull/3868
https://github.com/cs3org/reva/issues/3855