ci(*): consolidate image/chart workflow for prereleases for correct app version

[vdice]

For prereleases, we need to know the spin-operator image tag for injecting as the appVersion value in the corresponding Helm chart.

Thus, I've combined image build/publish with chart build/publish for prereleases (i.e. pushes to main) as a way to easily pass the tag down into the chart.

For now, I've left the duties of publishing v* charts in release.yaml since we upload the chart artifact to the GH release. However, this chart artifact could be argued as redundant since it exists in its ghcr.io form (and this is the source that all docs will advise to install from). Therefore, if we don't mind removing this artifact, we can consolidate all chart publishing logic into publish.yaml and reduce release.yaml to just uploading the crds and runtime-class manifests as artifacts and then creating the GH release itself. Thoughts?

[github-actions]

This PR now has an image available for testing:

  ttl.sh/spoopy-operator-pr-:24h

[endocrimes]

+1 to not bothering with attaching the chart to a github release unless there's eventual demand for it.

[endocrimes]

mostly lgtm - just looks like it probably needs a rebase

[vdice]

Thanks for the review @endocrimes.

Okay, after deliberating how to best orchestrate publishing of the image, chart and (if v* tag) create the GH release, it felt best to just add the GH release job to publish.yaml. I did this because I didn't want a GH release to be created without making sure both the image and the chart were successfully published. Rather than try to coordinate this dependency chain across workflows, I put 'em all in one. Definitely welcome ideas on a better future workflow state -- but this should get us what we need in the near term!

(Tested on my fork; see https://github.com/vdice/spin-operator/actions)

[vdice]

(markdown errors fixed in #103)