Update godoc.org references to use pkg.go.dev

[rifelpet]

pkg.go.dev will soon replace godoc.org. The main advantage of pkg.go.dev is that it is module-aware and version-aware, so one can view documentation for previous kops versions.

The only remaining references to godoc.org are these status widgets, which I dont believe are yet supported on pkg.go.dev:

grep -r godoc.org . | grep -v vendor
./docs/index.md:[GoDoc Widget]: https://godoc.org/k8s.io/kops?status.svg
./README.md:[GoDoc Widget]: https://godoc.org/k8s.io/kops?status.svg
./README-ES.md:[GoDoc Widget]: https://godoc.org/k8s.io/kops?status.svg

/area documentation

fixes #8371

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: rifelpet

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [rifelpet]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[johngmyers]

/retest

[johngmyers]

/retest
/lgtm