Enable static builds of flannel cni-plugin in RKE2

[rosskirkpat]

As part of enabling static builds of the flannel cni-plugin rancher/image-build-cni-plugins#2, the upstream build process needed to be completely revamped. These changes allow downstream consumption of a statically-linked flannel cni-plugin binary for both linux and windows.

Upstream PR: flannel-io/cni-plugin#22

[rosskirkpat]

The original PR and a few follow-up bug fixes have been merged. A new release of flannel-io/cni-plugin has been published.

Release Github Action: https://github.com/flannel-io/cni-plugin/actions/runs/1719455687
v1.0.1 Release page with automated release notes and binaries: https://github.com/flannel-io/cni-plugin/releases/tag/v1.0.1
Images published to Dockerhub under the v1.0.1 manifest: https://hub.docker.com/layers/flannelcni/flannel-cni-plugin/v1.0.1/images/sha256-e2396315d992b15a5e311e4ca76dfd0cfc9f98a91df4b22367f4b2d70ac69370?context=explore