[WIP] Enable building Windows container images

[sebsoto]

What type of PR is this?

/kind feature

What this PR does / why we need it:

Add basic functionality to build Windows images

Enables committing a Windows base image as the final layer.
This gives the possibility of building a Windows container image on a
Linux build system. Only COPY and ADD are in scope. This allows the
workflow of cross compiling Windows binaries on Linux, and copying them
into a Windows container image for use on Windows systems.

How to verify it

Which issue(s) this PR fixes:

Fixes #4010

Special notes for your reviewer:

Does this PR introduce a user-facing change?

[openshift-ci[bot]]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: sebsoto Once this PR has been reviewed and has the lgtm label, please assign mtrmac for approval. For more information see the Code Review Process.

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