fix: Close host on SIGINT

[MarcoPolo]

Closes #2785

This is closer to the old behavior prior to V0.34.

The first SIGINT closes the libp2p host. The second SIGINT follows the default Go behavior, unless the user is handling it.

This means, unless the user does something different, the default behavior will be 2 ctrl-c's are necessary to exit the program. I don't think this is perfect, but it's best we can do since FX will handle the first ctrl-c, and I don't think we should try to replicate the default Go behavior there. For now, I've added a log.Info to provide some info.

I'm open to other suggestions here.

[sukunrt]

Alternatively, we can expose the app.Done() channel and let users decide what to do with the signal. Users with more context can just call os.Exit after stopping the host and exit the program.

If I understand correctly previously, the default go signal handler terminated the program which users could override by registering their own signal handler.
If we make this change, users cannot override the behavior of stopping on ctrl+c

[richard-ramos]

I like the idea of exposing app.Done(), because then it would be possible to implement at the app level a behavior more natural of interrupting the app on a single SIGINT, compared to the proposal of having to press it twice

[MarcoPolo]

I think the real solution here is if fx didn't register signal handlers at all. This would allow users to:

• Rely on the default behavior of signals in Go programs.
• Handle signals in a standard Go way with signal.Notify.