Integration with nix-output-monitor when available

[RaitoBezarius]

Thank you for the amazing tool!

I would like to use nix-output-monitor for my local deployments, as they make the output nicer and more understandable.

What would the best way forward to send a PR on this?

I guess there is the parallel build matter, which I'm not sure how colmena handle it? Does it throw everything in a big list and let Nix build it? Therefore, nom should work out of the box?

[zhaofengli]

I think this is most easily done with the plain/verbose output style (-v) of Colmena where it doesn't try to redraw, so nix-output-monitor can print its fancy stuff. We can have a --nom mode (can be added here) that activates nom-specific behavior and launches nom during deployment, piping all output to it. At first glance, there are two things we need to change:

• Colmena launches a separate nix-build for each node (Build each node individually #47), with the outputs interleaved with each other. As a result, nom's human-readable message parser can get confused. I think we need to use the JSON-based parser and launch the builds with --log-format internal-json -v.
• With the plain output style, Colmena prefixes each line of output with the corresponding node name. This is helpful for users but doesn't work with nom's JSON parser. We need to drop the prefix if the event is stdout/stderr and the text starts with @nix.