WIP: file copy&paste using webdav

This marks the port org.spice-space.webdav.cb.0 as webdav channel.

See MRs for the other components for more details:

• spice-protocol!21 (closed)
• spice-gtk!54 (closed)
• spice/linux/vd_agent!13 (closed)
• https://gitlab.gnome.org/GNOME/phodav/-/merge_requests/16