With apk `--no-cache` parameter, there is no need to run `apk update`
and manually clean up the cache, apk will update automatically without
leaving local cache files to be cleaned up.
* `acme.sh`'s `ssh.sh` is probably one of the hooks that's most versatile
* By default, it's not installed on `alpine` docker images and therefore is lacking in the `acme.sh` docker image
* This change adds the `openssh` package and therefore the `ssh` and associated commands