Release automation

Releasing Kustomize is somewhat complicated because of the multiple modules involved. A fair amount of tooling exists in the repo to make this easier today. However, those tools are only usable by a small number of people in practice, and the process overall is still quite time-consuming.

Goals:
- [ ] The process should be as automated as possible. As much as possible should happen in remote tasks rather than on the maintainer's laptop.
- [x] Any Approver should be able to a release; the process should not require repo admin rights
- [ ] Existing SIG Release tooling should be re-used to the extent possible
- [x] Remove our reliance on an outdated GoReleaser version: https://github.com/kubernetes-sigs/kustomize/issues/4542
- [x] automate the kustomize-in-kubectl update [it is now scripted; does not necessarily happen immediately after release]
- [x] Improve release note generation to reference PRs appropriately https://github.com/kubernetes-sigs/kustomize/pull/4537

/triage accepted
/area release