Easier-to-browse logs in CI

[epage]

Modern CIs group all of the output for a command, making it easy to see cause-and-affect but this breaks down when there are "do everything" commands.

Some CI systems support special output directives so commands can provide their own grouping, e.g. github. I feel like detecting a CI system and emitting these directives would improve the experience of using cargo-hack.

Downsides

• Piecemeal support for different CI systems as they implement it and cargo-hack supports it
• Raw logs will have extra chatter

[taiki-e]

Thanks for the suggestion! I've experimented with this in #206, and it looks great.

https://github.com/taiki-e/cargo-hack/actions/runs/6098364195/job/16548664583#step:7:25