[FR]: py_image_layer

[alexeagle]

What is the current behavior?

Users have to paste some starlark into their projects.

Describe the feature

I think we can get to a public API similar to js_image_layer that we're able to commit to, and add to this repository.

[thesayyn]

Note that now we have bsdtar toolchain in bazel-lib, we can do this with no runtime code needed.

[alexeagle]

I want this now to make aspect init nice: aspect-build/aspect-workflows-template#60