feat: Include gitops-promoter release changelog in ArtifactHub annotations

[Copilot]

ArtifactHub supports an artifacthub.io/changes annotation to surface per-release changelogs. This wires up the gitops-promoter GitHub release notes to populate that annotation automatically during version updates.

New: hack/update-artifacthub-changes.sh

• Fetches the release body for a given gitops-promoter tag from the GitHub API
• Parses Markdown release notes (embedded Python): maps section headers to ArtifactHub kind values (added, fixed, changed, removed, deprecated, security), falls back to keyword detection on bullet text for generic "What's Changed" sections
• Extracts PR/issue URLs into the links field; strips by @author in https://... noise from descriptions
• Skips "New Contributors" and "Full Changelog" sections
• Patches chart/Chart.yaml via yq; exits with a warning (non-fatal) if the release has no body or yields no parsed entries

Updated: update-gitops-promoter-version.yaml

Adds a step between CRD annotation update and PR creation that calls the new script:

- name: Set Artifact Hub changes annotation from gitops-promoter release notes
  working-directory: current-repo
  run: |
    bash hack/update-artifacthub-changes.sh \
      --version "${{ steps.get-latest-release.outputs.latest_version }}" \
      --github-token "${{ secrets.GITHUB_TOKEN }}"

Example of what gets written to Chart.yaml:

artifacthub.io/changes: |-
  - kind: fixed
    description: Resolve race condition in reconciler
    links:
      - name: GitHub PR
        url: https://github.com/argoproj-labs/gitops-promoter/pull/100
  - kind: added
    description: Support GitHub Enterprise
    links:
      - name: GitHub PR
        url: https://github.com/argoproj-labs/gitops-promoter/pull/200

Original prompt

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This section details on the original issue you should resolve

<issue_title>Include change info in ArtifactHub annotations</issue_title>
<issue_description>ArtifactHub supports an annotation in Chart.yaml to specify changes that happened in a given release.

We should pull changelog info from the GitHub releases of gitops-promoter to populate that annotation during the release workflow.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Include change info in ArtifactHub annotations #52

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