fix(redirects): forward k8s.io Go package URLs to pkg.go.dev

[singhvishalkr]

Issue #55628 reports that https://kubernetes.io/api, /apimachinery, and /client-go all 404. Browsers reach these paths through the k8s.io Go vanity URLs: k8s.io/api serves the go-import meta tag for go get, but a browser hitting the same URL gets a normal 302 to kubernetes.io/api and dead-ends there.

The reporter suggested forwarding these to pkg.go.dev/k8s.io/{package}, which is where the canonical Go package documentation lives. This PR does exactly that with three 301 entries in static/_redirects.base:

/api          https://pkg.go.dev/k8s.io/api          301
/apimachinery https://pkg.go.dev/k8s.io/apimachinery 301
/client-go    https://pkg.go.dev/k8s.io/client-go    301

/api, /apimachinery, and /client-go are not currently published as kubernetes.io content, so there is no conflicting page to override. The 301 status follows the convention used by the existing site-internal entries in the same file; the external-redirect form follows the precedent of /docs/tasks/tools/install-minikube/ -> https://minikube.sigs.k8s.io/docs/start/.

Scope is intentionally narrow: only the three paths called out in the issue. Sub-path splat redirects (e.g. /api/core/v1/* -> pkg.go.dev/k8s.io/api/core/v1/...) are easy to add later if a maintainer thinks they are worth it, but the issue is specifically about the package landing pages and I did not want to expand surface beyond what was reported.

Closes #55628

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[singhvishalkr]

/assign @SayakMukhopadhyay

[lmktfy]

Thanks; I suggest a tweak. Use 307 rather than 301 status for the redirects.

I also don't know if we want to make this change. Anyway, it is almost technically correct, and the fixup is easy.

[Arhell]

Lgtm

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[singhvishalkr]

Switched to 307 in fbdc901. Makes sense since pkg.go.dev could change its URL scheme.