Ensure Watchtower removes old images

The github runner machine ran our of disk space because of old runner images.
This should ensure that doesn't happen any more :o)

Signed-off-by: Matt Spencer matthew@thespencers.me.uk

frontend.yaml

@@ -112,6 +112,7 @@
           - /var/run/docker.sock:/var/run/docker.sock
           - /home/matt/.docker/config.json:/config.json
         command:
+          - --cleanup
           - --http-api-update
           - --http-api-token={{ secrets.WATCHTOWER_HTTP_API_TOKEN }}
           - --http-api-periodic-polls