chore: add utilities for Windows Docker image publishing

[CaerusKaru]

Currently, Buildbarn repos publish the artifacts from
cross-compiled builds of the various ecosystem binaries. However,
this leaves the user to manage pulling those artifacts and
distributing/consuming them in their respective environments. For
customers leveraging Kubernetes or other containerized settings,
this creates a greater burden than Linux consumers.

In a previous commit, the image handling was moved to rules_img,
however rules_img does not allow for the necessary manifest
layering to include a Windows image (with a distinct base layer).
Therefore, we add an additional macro that reverts back to the
original rules_oci publish stream, until rules_img can be updated
to support that behavior. For images that do not benefit from a
Windows build-out (e.g. the non-RBE images), the new path can
still be safely utilized.

[aspect-workflows]

Test

All tests were cache hits

29 tests (100.0%) were fully cached saving 6s.

[EdSchouten]

In a previous commit, the image handling was moved to rules_img, however rules_img does not allow for the necessary manifest layering to include a Windows image (with a distinct base layer).

Can't we fix rules_img to support this?

[CaerusKaru]

Can't we fix rules_img to support this?

Of course we can, but I don't maintain that library, nor do I have the time to manage such a fix. What I do know is that rules_oci works for this case, and the way I've structured this commit, a) most images will continue to use it; and b) once it is patched, it would be trivial to move the images we do apply this to back to it.

[EdSchouten]

@malt3 Would you happen to have any input on this matter?

[malt3]

I believe we do support Windows, but there may be issues when combining separate base images on different platforms (where those do not use a common image index).
Happy to add support for this soon-ish, but I don't want to block any important features from being added to Buildbarn.