Automate release via GH Action

[CecileRobertMichon]

/kind feature

We should automate as much of the release process as possible to avoid human error. The current release steps are fairly automated but still require a maintainer to go through them one by one: https://capz.sigs.k8s.io/developers/releasing.html

Easy win: We should add a Github Action that does all the artifact generation and upload as well as release notes generation when a tag is created.

Longer-term: how can we automate the process of opening PRs to promote images?

[CecileRobertMichon]

@jackfrancis I might bug you for some tips on this since you've gone through the process recently

[CecileRobertMichon]

/assign