autoprovision: split script+unit into separate files

Now that we're using Jinja to render the kickstart scripts, we can
separate out scripts, systemd unit files, etc. into their own files and
`include` them.  This makes editing them much easier, especially since
syntax highlighting will work correctly.

notify-online.sh

@@ -0,0 +1,13 @@
+#!/bin/sh
+
+set -- \
+    -F "hostname=$(hostname -f)" \
+    -F 'sshkeys=<-;type=text/plain'
+
+fw_cfg=/sys/firmware/qemu_fw_cfg/by_name/opt/dch/cfg-branch/raw
+if [ -r "${fw_cfg}" ]; then
+    set -- "$@" -F branch="$(cat "${fw_cfg}")"
+fi
+
+cat /etc/ssh/ssh_host_*_key.pub \
+    | curl -fsS https://webhooks.pyrocufflink.blue/host/online "$@"