Make log command extensible internally

[rosecodym]

Description:

I'm experimenting with ways to manipulate the git log that's being used to generate diffs (specifically, limiting its depth in come cases). Tweaking RepoPath for this locally isn't a huge deal but making the log command extensible seems like it could generally be useful, so I figured I'd do it.

Checklist:

• Tests passing (make test-community)?
• Lint passing (make lint this requires golangci-lint)?

[zricethezav]

@rgmz caught a gotcha with user defined git log options: gitleaks/gitleaks#1153. We might want to introduce something similar here if we think users are gonna go wild with it

[rosecodym]

@rgmz caught a gotcha with user defined git log options: gitleaks/gitleaks#1153. We might want to introduce something similar here if we think users are gonna go wild with it

If I'm reading that right, we already separate our logs opts into separate argument to exec.Command, but that's a really good thing to know!

[rosecodym]

Oh, I but I should ensure that additionalArgs are appended before the -- option, if it exists.