Resolve "Add Upstream Release Notes section to the `README.md.gotmpl` so that renovates can link to it consistently"

General MR

Summary

While working through renovate-runner#30 as part of the automate renovate ticket workflow epic, I submitted manual README updates to a number of BigBang packages. As you might expect, those started to break once maintainers reran their README generation scripts using the templates in this repository.

This MR updates the templates we all use to (re)generate our packages' README.md files so that upstream release notes can be pulled out of chart/Chart.yaml if they are logged using an annotation of this form:

annotations:
  bigbang.dev/upstreamReleaseNotesMarkdown: |
    - [Find our upstream chart's CHANGELOG here](https://link-goes-here/CHANGELOG.md)
    - [and our upstream application release notes here](https://another-link-here/RELEASE_NOTES.md)

Relevant logs/screenshots

Happy path - gitlab package

• ✅ release notes link shows up as expected
• ✅ the leading "don't edit this file by hand" comment doesn't render in the browser

New footer with some "use gluon please" breadcrumbs

Sad path

If there is no bigbang.dev/upstreamReleaseNotesMarkdown key in a package's chart/Chart.yaml, the default output explains that there's no upstream release notes annotation in Chart.yaml for this package and describes how to accomplish that:

Linked Issue

N/A

Upgrade Notices

BigBang package maintainers will want to update their local helm-docs readme updater scripts to use version 1.14.2, up from the 1.10.0 we used previously.

Closes #43 (closed).