it builds the docker image and pushes it to the hardcoded registry

since we place configs (which could be yaml) in the lubidock
repository it can cause errors while mistakenly parsing service
configs instead of only parsing compose files

fixes issue #1

otherwise they won't work locally on the swarm workers

this matches the version used on our hosts
-preview is used because buster (including the newer nf_tables backend for iptables) isn't available in stretch

this orders the SWARM-NAT jump rule before DOCKER-INGERSS

This commit adds Get-DockerIngressAddress

this strips away some splatting boilerplate of the other iptables functions

this is done by two functions:
Test-IptablesChain
Add-IptablesChain