Stop hardcoding 10.42.0.1 everywhere... use DNS!

Since we need to use our own dnsmasq for the firewall, it could be a good idea to start using it to replace hardcoded IPs with DNS names such as:

• executor.(local|$farm.ci-farm)
• salad.(local|$farm.ci-farm)

This would allow us to connect to multiple farms using wireguard, and we could select which executor to target using:

$ executorctl -e http://executor.mupuf.ci-farm run job.yml

or, when I add this new flag in executorctl:

$ executorctl -f mupuf run job.yml

We could also have a config file for executorctl that would list the different farm names. This would allow us to query the list of machines (and their tags), and on which farm they are. This would also allow us to not have to specify a farm, and executorctl would find a farm with what is wanted by devs.

How does this sound?