feat: .git/info/exclude support in init

[tuncbkose]

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Adds #466 via -gl/--gitignore_local flag (I didn't know what else to name it).

This will only work if the current directory (as opposed to a given target) is a git repo, and silently fall back to .gitignore otherwise. I chose to do so because devenv currently seems to write .gitignore only in the current directory as well.

I'm not sure how/where to add a test, but will happily make one if someone tells me.

[domenkozar]

I'm a bit puzzled, what's the use case for .git/info/exclude?

[tuncbkose]

I gave an example in the linked issue. If that is not convincing enough, I don't have a better one