git clean is destructive and undocumented

[nojnhuh]

I have some gitignored local configuration I maintain locally in the same directory as a git repo. Running go-apidiff irrecoverably deletes all of those files because of the git clean it does here:

go-apidiff/pkg/diff/run.go

Lines 199 to 201 in 00f8d2e

	if err := wt.Clean(&git.CleanOptions{Dir: true}); err != nil {
	return nil, nil, err
	}

This behavior is destructive and essentially impossible to know about until it's too late. This behavior should be documented and put behind a descriptive flag like --force-clean.