Consolidate Github release management in one step

[mgoerens]

~Please do not review/merge just yet, I want to see the pipeline results before testing/applying further code optimizations~ READY !

So far the chart-repo-manager script had multiple functions:

• Create the GitHub Release (only if the chart's sources are provided) using chart-releaser.
• Prepare the index entry for this chart.
• Update the Helm repository index.

In addition, a separate step in our build.yaml workflow added the report.yaml to the GitHub release (potentially creating it, in the case the chart's sources are not provided).

This commit brings the following changes:

• Reduce the role of the chart-repo-manager script to a) the preparation of all artifacts that go into a GitHub Release, and b) the crafting of the index entry.
• Consolidate the GitHub release creation and the upload of all its artifacts into a single step. This eliminates the need to use chart-releaser.
• Create a dedicated step for the update of the Helm repository index.
• Favor running shell commands directly in the steps 'run:' rather than in the python scripts, using subprocesses. This is expecially true for the multiple "git" commands used to update the index.

This makes https://github.com/openshift-helm-charts/charts/issues/1080 obsolete and can be closed.

---

Note for reviewers: To be discussed but there is room for further improvement, for instance:

• The step that updates the index is quite large due mostly to the use of shell commands over python subprocesses, and could be split into smaller more readable steps.
• We could reconsider the need to create a worktree vs checkout the index branch.

[komish]

@mgoerens one last question here (aside from those already in-lined):

I see this log line being emitted in the step where the github release and index entries are being prepared (read: not created).

[INFO] Helm package was released at https://github.com/openshift-helm-charts/sandbox/releases/download/hashicorp-25bc8561e1b34b06985003c84efe4963-289-vault-0.17.0/vault-0.17.0.tgz

https://github.com/openshift-helm-charts/sandbox/actions/runs/6810139895/job/18517922140#step:9:195

Are we emitting this, a tool we're calling, or is this a remnant from when we called chart-releaser?

[EDIT] Looks like we emit it here? https://github.com/openshift-helm-charts/development/blob/8020679fba4c2cf8acd7f9f10ba7d1848f18e652/scripts/src/chartrepomanager/chartrepomanager.py#L473

Happy to have this fixed later if need be. Marking LGTM.

[mgoerens]

@komish Good catch, I removed it as in the next step "Create GitHub release" we also have the URL for this release printed out, e.g.

🎉 Release ready at https://github.com/openshift-helm-charts/sandbox/releases/tag/hashicorp-25bc8561e1b34b06985003c84efe4963-289-vault-0.17.0

I also doubled check the other INFO/DEBUG messages and I added one missing INFO message was previously present:

          echo "[INFO] Add and commit changes to git"

in build.yaml before pushing the changes to the index branch.