feat: Add validation task for NGINX modules and installing NGINX Plus HA keepalived module

[alessfg]

Proposed changes

• Add support for installing the NGINX Plus HA keepalived module.
• Add validation tasks to check the Ansible version, the Jinja2 version, whether the required Ansible collections for this role are installed, and whether you are trying to install a valid NGINX module.

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).