Support ignoring arbitrary paths

[moschlar]

I'd like to be able to specify some additional file paths that should be ignored when diffing, like /var/log/dpkg.log on Debian/Ubuntu images which will contain differing log timestamps even if the exact same packages had been installed.

(Of course, my workaround is to simply drop these logfiles from the image, but still - there might be other use cases)

[mzihlmann]

Implemented in my fork here as I use it for kaniko testing. It's part of the "extra-ignores" I need to make kaniko & buildkit output somewhat compatible. If you want I can open a PR for it here.

mzihlmann@8086800