Rename debian.interfaces to ifupdown

When I first split the debian interfaces support from wwinit, I was unable to
figure out what it was called. I used the inelegant name "debian.interfaces" to
identify it; but I have since learned that it is called "ifupdown." I have
since learned that there is even a variant implementation, ifupdown-ng, that is
used by Alpine Linux.

This PR renames the overlay to ifupdown, but retains a copy of it at
debian.interfaces for backwards compatibility.

Signed-off-by: Jonathon Anderson <janderson@ciq.com>

etc/nodes.conf

@@ -15,8 +15,8 @@ nodeprofiles:
       - udev.netname
       - systemd.netname
       - ifcfg
+      - ifupdown
       - NetworkManager
-      - debian.interfaces
       - wicked
       - ignition
     kernel: