Split Release workflow job into multiple, retryable jobs

[snazy]

The Nessie release for 0.83 failed two times, we had to re-release as 0.83.1 and finally 0.83.2, beacuse the release-publish workflow is not retryable, mostly because multiple publications of Maven artifacts of the same versions are not possible.

This change splits the single workflow job into multiple:

Prepare -->--+
             |
             +-->-- Publish to Maven Central -->--+
             |                                    |
             +-->-- Publish OpenAPI ----------->--+
             |                                    |
             +-->-- Publish Docker images ----->--+
             |                                    |
             +-->-- Publish Helm Chart -------->--+
                                                  |
                                                  +-->-- GitHub Release notes

This change also moves the big script to create the GH release notes to a separate shell script.

Fixes #8581

[XN137]

not easy to review the diff but nothing stood out as wrong/missed.

wondering though:
if any of the sub-jobs is eventually not retry-able for whatever reason, do we end up with a "worse" release state compared to previously (i.e. partially published artifacts) or is the result equally bad as the "single flow" we had before?
(and we dont advertise that version as usable)

[snazy]

if any of the sub-jobs is eventually not retry-able for whatever reason, do we end up with a "worse" release state compared to previously (i.e. partially published artifacts) or is the result equally bad as the "single flow" we had before?

I don't think it's worse than before. The only non-retryable part is the Maven publication. We already had a few "failed releases", where only some targets succeeded.