Introduce test/e2e_node_windows/ as a self-contained Windows node e2e
test suite, fully isolated from the Linux-focused test/e2e_node/ package.
All new files are gated with //go:build windows, and the tree includes
a scoped OWNERS file so it lands under an agreed governance model.
In hack/lib/golang.sh, skip building test/e2e_node/e2e_node.test when
KUBE_BUILD_PLATFORMS targets Windows. Windows has a separate e2e_node
test binary which does not currently need to be bundled in an archive.
Document the Windows feature label in test/e2e/feature/feature.go.
