chore: add artifacthub.io/changes changelog annotation to the released chart

[lemeurherve]

This PR adds Artifact Hub annotation in the released chart so it can renders its integrated changelog: https://blog.artifacthub.io/blog/changelogs/

Notes:

• Only the current version changes have to be included, not the full changelog.

• It's the simple form of Artifact Hub changes. Looking at the existing changelog, I'm not sure the more complete form will ever be needed.

• I had to strip emojis to avoid having the scalar value broke as single string and failing chart-releaser step:

  📦 Add `artifacthub.io/changes` changelog annotation to the released chart.
  
  Table example:
  | plugin                | old version          | new version           |
  |-----------------------|----------------------|-----------------------|
  | kubernetes            | 3900.va_dce992317b_4 | 3937.vd7b_82db_e347b_ |
  | configuration-as-code | 1625.v27444588cc3d   | 1647.ve39ca_b_829b_42 |
  

  replaced by

  artifacthub.io/changes: "\U0001F4E6 Add `artifacthub.io/changes` changelog annotation to the released chart.\n\nTable example:\n| plugin                | old version          | new version           |\n|-----------------------|----------------------|-----------------------|\n| kubernetes            | 3900.va_dce992317b_4 | 3937.vd7b_82db_e347b_ |\n| configuration-as-code | 1625.v27444588cc3d   | 1647.ve39ca_b_829b_42 |"
  

• I'm using yq to retrieve the version directly from Chart.yaml, easier than the previous method requiring two steps.

Tested on a fork:

• Entry in CHANGELOG.md starting with an emoji and including a table: https://github.com/lemeurherve/jenkinsci-helm-charts/blob/862770b35ef457f3ffc20b6286e227ee74fef91f/charts/jenkins/CHANGELOG.md?plain=1

• Release: https://github.com/lemeurherve/jenkinsci-helm-charts/releases/tag/jenkins-4.8.4

• Released Chart.yaml content

  annotations:
    artifacthub.io/category: integration-delivery
    artifacthub.io/changes: |-
      Add `artifacthub.io/changes` changelog annotation to the released chart.
  
      Table example:
      | plugin                | old version          | new version           |
      |-----------------------|----------------------|-----------------------|
      | kubernetes            | 3900.va_dce992317b_4 | 3937.vd7b_82db_e347b_ |
      | configuration-as-code | 1625.v27444588cc3d   | 1647.ve39ca_b_829b_42 |
    artifacthub.io/images: |
      - name: jenkins
        image: jenkins/jenkins:2.426.1-jdk11
      - name: k8s-sidecar
        image: kiwigrid/k8s-sidecar:1.24.4
      - name: inbound-agent
        image: jenkins/inbound-agent:3107.v665000b_51092-15
      - name: backup
        image: maorfr/kube-tasks:0.2.0
    artifacthub.io/license: Apache-2.0
    artifacthub.io/links: |
      - name: Chart Source
        url: https://github.com/jenkinsci/helm-charts/tree/main/charts/jenkins
      - name: Jenkins
        url: https://www.jenkins.io/
      - name: support
        url: https://github.com/jenkinsci/helm-charts/issues
  apiVersion: v2
  appVersion: 2.426.1
  description: Jenkins - Build great things at any scale! The leading open source automation
    server, Jenkins provides over 1800 plugins to support building, deploying and automating
    any project.
  home: https://jenkins.io/
  icon: https://get.jenkins.io/art/jenkins-logo/logo.svg
  keywords:
  - jenkins
  - ci
  - devops
  maintainers:
  - email: [email protected]
    name: maorfr
  - email: [email protected]
    name: torstenwalter
  - email: [email protected]
    name: mogaal
  - email: [email protected]
    name: wmcdona89
  - email: [email protected]
    name: timja
  name: jenkins
  sources:
  - https://github.com/jenkinsci/jenkins
  - https://github.com/jenkinsci/docker-inbound-agent
  - https://github.com/maorfr/kube-tasks
  - https://github.com/jenkinsci/configuration-as-code-plugin
  version: 4.8.4
  

Follow-up of:

• chore: add last version changelog to the GitHub release #946 (review)

Submitter checklist

Preview Give feedback

1. I bumped the "version" key in ./charts/jenkins/Chart.yml.
2. I added a new changelog entry to ./charts/jenkins/CHANGELOG.md.
3. I followed the technical requirements.

Special notes for your reviewer

[timja]

wow nice!

[hervelemeur]

I need to prepare a fixup to properly quote the changelog if it contains only one line.