This adds (incomplete) support for configuring the BGP backbone that
could until now only be deployed locally using shell scripts.

The idea is to share the CSV-based config files between the shell
scripts and the new Ansible-based approach to allow peaceful coexistence
of both deployment variants. Note that the Ansible-based approach
verifies input data much stricter than the shell scripts to prevent
common user errors, so not everything will work.

For Ansible to find the config CSVs, a symlink "backbone-conf" to the
conf directory of the backbone repo[1] is expected in the ansible root
directory.

Currently, the ansible-based approach can only deploy Wireguard tunnels,
but will be extended to also configure Bird2 sessions.

[1] https://github.com/freifunk-stuttgart/backbone

role revproxy: allow additional configuration, check host_vars/revproxy.as208772.net/revproxy -> unifi.freifunk-stuttgart.de for an example

one should use the ffs11.pveadmin.freifunk-stuttgart.de

hostnames no longer exist and prevent renewal for other hosts