feature: minidump-stackwalk cyborg output

[Gankra]

Currently you can only get human output or machine (json) output. While you could run the tool twice, this is fairly wasteful. Ideally we would have a cyborg output mode that does both.

The main issue is that current minidump-stackwalk only has the notion of one "output". You can specify whether that's stdout or --output-file, but it's still just one output.

The simplest solution is this tentative syntax:

--cyborg=path/to/write.json

I figure in typical usage you want the human output to still hit stdout, so keeping the human output as the "default" output that goes to stdout (and can still be configured with --output-file) makes the most sense to me?

This would be useful for https://bugzilla.mozilla.org/show_bug.cgi?id=1487410

[Gankra]

Implemented in #316