feat!: Remove Alpine 3.17 and add Alpine 3.21

[alessfg]

Proposed changes

Add support for installing NGINX Open Source and NGINX Plus on Alpine Linux 3.21 and remove support for installing NGINX Plus on Alpine Linux 3.17.

Checklist

Before creating a PR, run through this checklist and mark each as complete:

• I have read the contributing guidelines.
• I have signed the F5 Contributor License Agreement (CLA).
• If applicable, I have added Molecule tests that prove my fix is effective or that my feature works.
• If applicable, I have checked that any relevant Molecule tests pass after adding my changes.
• I have updated any relevant documentation (defaults/main/*.yml, README.md and CHANGELOG.md).

[Copilot]

Pull Request Overview

This PR removes support for Alpine Linux 3.17 and integrates Alpine Linux 3.21 support across the role and its associated Molecule tests, updating the configuration and documentation accordingly.

• Update supported Alpine versions in vars/main.yml for both NGINX Open Source and NGINX Plus
• Add new Alpine 3.21 platforms in various Molecule configuration files
• Adjust CHANGELOG to reflect the breaking change and feature additions

Reviewed Changes

Copilot reviewed 12 out of 16 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
vars/main.yml	Updated supported Alpine versions and adjusted SLES versions
molecule/version/molecule.yml	Removed Alpine 3.17 and added Alpine 3.21 platform
molecule/upgrade/molecule.yml	Added Alpine 3.21 platform
molecule/upgrade-plus/molecule.yml	Updated comment regarding Alpine version support
molecule/uninstall-plus/molecule.yml	Added Alpine 3.21 platform
molecule/stable/molecule.yml	Added Alpine 3.21 platform
molecule/source-version/molecule.yml	Added Alpine 3.21 platform
molecule/plus/converge.yml	Removed opentracing from the list of modules
molecule/downgrade/molecule.yml	Added Alpine 3.21 platform
molecule/downgrade-plus/molecule.yml	Revised Alpine platform entries and comments
molecule/default/molecule.yml	Added a new Alpine platform, but with a version mismatch
CHANGELOG.md	Updated version and breaking change notes

Files not reviewed (4)

• molecule/distribution/molecule.yml: Language not supported
• molecule/plus/molecule.yml: Language not supported
• molecule/source/molecule.yml: Language not supported
• molecule/uninstall/molecule.yml: Language not supported

Comments suppressed due to low confidence (1)

molecule/default/molecule.yml:46

• The platform is named 'alpine-3.21' but the Docker image is set to 'alpine:3.22'. Please verify whether this is intentional or adjust the image version to match the platform name.

    image: alpine:3.22