The dockhand-updater image ships Docker CLI 29.2.1 (API 1.53), which
fails on hosts running older Docker daemons (e.g. Synology DSM with
Docker 24.0.2 / API 1.43). Every docker command in update.sh returns
"client version 1.53 is too new".
Query the daemon's API version via /version and pass it as
DOCKER_API_VERSION to the updater container env. If the env var is
already set on the main container, forward that instead.
Fixes#759
