Add Helm chart OCI release to GH automation

[inteon]

Adds logic for pushing the Helm chart to an OCI registry (and adding a non-v-prefixed tag)

See cert-manager/makefile-modules#219 for more info.

[wallrj]

Thanks. It looks like that instruction to manually upload the Helm chart was already out of date
The Helm chart was being added to the draft release by the upload-artifact action.
This PR removes that feature, presumably because you think it is redundant. I agree.

I can't see any evidence of a test release, so I presume that you will test this after it merges.

/approve
/lgtm

[cert-manager-prow]

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[cert-manager-prow]

New changes are detected. LGTM label has been removed.