Backup volumes from host instead of copying paths

* Backupbot will now copy all volumes from a service with
  backupbot.enabled = 'true' label from the /var/lib/docker/volumes/
  path directly. This reduces the resource overhead of copying
  stuff from one volume to another.
  Recipes need to be adjustet that db-dumps are saved into a volume
  now!
* Remove the Dockerfile and move stuff into a entrypoint. This
  simplifies the whole versioning thing and makes this "just"
  a recipe

Co-authored-by: Moritz < moritz.m@local-it.org>

entrypoint.sh

@@ -0,0 +1,12 @@
+#!/bin/sh
+
+set -e
+
+apk add --upgrade --no-cache bash curl jq restic
+
+cron_schedule="${CRON_SCHEDULE:?CRON_SCHEDULE not set}"
+
+echo "$cron_schedule /backup.sh" | crontab -
+crontab -l
+
+crond -f -d8 -L /dev/stdout