- runtime base image from s6-base(deb11) to s6-overlay-lite(deb12)
 - update kresd package repo url
 - openvpn from 2.5.1 -> 2.6.3

We'll run obfs4 bridge processes in a separate obfsvpn container which
can be colocated with the openvpn gateway or hosted separately.

Additionally removes some out of date documentation.

The upstream openvpn-exporter was emitting high cardinality metrics, because of
the CN being an unique identifier based off of the certificate. This would cause
the tsdb to fill with unnecessary, and unrelated metrics.

This removes that exporter (which has not seen commits for years) and replaces
it with the prometheus-node-exporter textfile collector, which will emit metrics
produced by the shell script that is run every 10 seconds. It will only emit
these metrics:

openvpn_server_connected_clients{status_path="/tmp/openvpn-status-tcp"}
openvpn_server_connected_clients{status_path="/tmp/openvpn-status-udp"}
openvpn_up{status_path="/tmp/openvpn-status-tcp"}
openvpn_up{status_path="/tmp/openvpn-status-udp"}

The version in Debian is very old and has issues.

We revert to shapeshifter-dispatcher because obfsvpn is not working yet, and we
also do not need vpnwatch.

iproute2 needs to be explicitly installed, the iptables alternative needs to
iptables-legacy.

We need 2.5 for block-ipv6

use the stretch image, at least until #2 is fixed.

We add the http module so we can get prometheus metrics as well.

build is fixed

use go 1.13 so it can utilize go modules

Upstream doesn't have proper releases, and they are breaking master causing
breakage in our pipelines

not a regular (non-symlink) file

/sbin/ip is a symlink to /bin/ip