sources to support reading an `ignore`, and looking at the opposite of what's ignored

[ghostsquad]

I found myself writing this:

  docker:bake:
    deps:
    - docker:create-multiarch-builder
    # this should match what's in .dockerignore
    sources:
    - ./cmd/**/*
    - ./internal/**/*
    - ./proto/**/*
    - ./testdata/**/*
    - ./go.*

with a .dockerignore file of:

*
!cmd/
!internal/
!proto/
!testdata/
!go.*

and thought, wouldn't it be nice if...

[trulede]

This can be resolved using a similar technique as mentioned in #88 and provided by pr #2671