new(k0sproject.io/k0s): zero-deps Kubernetes distribution

[tannevaled]

Summary

Adds a pantry recipe for k0s, k0sproject's single-binary CNCF-class Kubernetes distribution (sibling to the existing k0sctl recipe).

• Builds from source via the upstream Makefile.
• EMBEDDED_BINS_BUILDMODE=none skips the Docker-based build of embedded kubelet/etcd/containerd/runc/kine/konnectivity (pantry CI has no Docker daemon). The resulting k0s CLI still ships the full code, with third-party node binaries supplied out of band (e.g. airgap bundle).
• VERSION is passed explicitly because the upstream Makefile uses git describe --tags, which fails inside a tarball checkout.
• Restricted to linux/x86-64 and linux/aarch64; the upstream Makefile pins TARGET_OS=linux and k0s is a Linux-node distribution.

Test plan

• CI builds on linux/x86-64
• CI builds on linux/aarch64
• k0s version matches the tag
• k0s --help produces help output

[tannevaled]

Iter 4 progress: version-parser fixed (`+k0s.N` strip in commit `c7ebc727`), but now blocked on Docker dependency for code generation.

The recipe's earlier `EMBEDDED_BINS_BUILDMODE=none` correctly bypasses the Docker build for embedded kubelet/etcd/containerd/runc/kine/konnectivity components. However, k0s's Makefile ALSO uses a Docker image (`.k0sbuild.docker-image.k0s`) as the build host for code-generation steps (`controller-gen`, `client-gen`, `gen-bindata`).

```
make: *** [Makefile:135: .k0sbuild.docker-image.k0s] Error 127
```

Error 127 = command not found (`docker` is not in pantry's CI environment).

What would unblock this

Three paths, none small:

1. Bypass make + run codegen directly via Go. The Makefile delegates to `$(GO) run` for codegen, but those invocations have `.k0sbuild.docker-image.k0s` as a prereq. Would require replicating the codegen pipeline in the recipe shell script — significant maintenance burden as k0s's codegen evolves.

2. Vendor the generated code. Pre-generate the codegen outputs upstream and check them into a release branch or distributable tarball. Upstream maintains the docker-based pipeline; pantry would need a custom tarball.

3. Add docker to pantry's CI runner. Systemic change affecting the whole pantry, requires maintainer buy-in (and probably won't happen — docker-in-CI is heavy and pantry's bottle build approach is intentionally docker-free).

Recommendation

Park this PR with the current state (version-parser fix is documented and reusable). Same pattern as #13141 (open-vcdiff) and #13131 (Neon). The k0s server is a multi-component K8s distribution that genuinely needs orchestrated tooling — pantry's single-recipe model doesn't map.

`k0sctl` (the cluster-launcher CLI) is already in pantry at `projects/github.com/k0sproject/k0sctl/` — that's the user-facing tool. Users wanting to RUN k0s on Linux nodes can install the upstream tarball directly via their distro or k0s's own installer script.

Closing as wontfix if no maintainer objection.