If a change to one of the tracked files happened soon after (<1 second?)
a previously detected change, it could end up going undetected. In
particular, this could cause integration tests to fail (see next
commits).
Fixed by computing the new checksum file _before_ checking for changes.
Will extract certificates from acme.json as written by traefik for usage in dovecot and postfix.
Also watches acme.json for changes. For this to work the file has to be mounted/present at `/etc/letsencrypt/acme.json`