Adding signal type to onSignal function

[Sammyjroberts]

terminus/lib/terminus.js

Line 143 in c1a26fb

await onSignal()

->

await onSignal(signal)

For observability I like to track what signal caused the graceful shutdown, could we add the signal as a parameter to onSignal?
I'd be willing to make the PR if that would be helpful

[rsaryev]

Coincidentally, I've already submitted a merge request that adds the signal as a parameter to onSignal, addressing your concern. Feel free to check it out and share your thoughts!

#327