fix(prometheus): use ansible_facts for fqdn

[willbuckner]

Summary

• Replace injected ansible_fqdn references with ansible_facts['fqdn'].
• Update the Prometheus defaults and corresponding argument specifications.
• Update the alternative Molecule scenario.
• Preserve the existing ansible_host, inventory_hostname, and localhost fallbacks.

Motivation

This fixes a deprecation warning I was seeing on my own Ansible deployments. The default behavior of injecting facts as top-level variables is deprecated and will be removed in ansible-core 2.24.

Reading fqdn directly from ansible_facts avoids the deprecation warning and works when inject_facts_as_vars is disabled.

This is a follow-up to #845.

Validation

• ansible-lint and yamllint passed with zero failures or warnings.
• Verified with ansible-core 2.21.2 that the deprecation warning disappears.
• git diff --check passed.

[github-actions]

Docs Build 📝

Thank you for contributing!✨

This PR has been merged and the docs are now incorporated into main:
https://prometheus-community.github.io/ansible/branch/main

[SuperQ]

Thanks!

[willbuckner]

Any idea what's going on with this second set of integration test failures here?

  Aug 07 08:49:52 fed2fb714349 systemd[1]: Dependency failed for Docker Application Container Engine.
  Aug 07 08:49:52 fed2fb714349 systemd[1]: docker.service: Job docker.service/start failed with result 'dependency'.
  Setting up dnsmasq-base (2.90-0ubuntu0.20.04.1) ...
  Setting up ubuntu-fan (0.12.13ubuntu0.1) ...
  Created symlink /etc/systemd/system/multi-user.target.wants/ubuntu-fan.service → /lib/systemd/system/ubuntu-fan.service.
  Processing triggers for systemd (245.4-4ubuntu3.18) ...
  Processing triggers for libc-bin (2.31-0ubuntu9.9) ...
  Processing triggers for dbus (1.12.16-2ubuntu2.3) ...
  ERROR    Failed to validate /root/ansible_collections/prometheus/prometheus/roles/prometheus/molecule/alternative/molecule.yml
  

I'm investigating but it doesn't seem related to my change.

[willbuckner]

CI failures diagnosis: #869 (comment)

[willbuckner]

@SuperQ this one is rebased on top of your CI fixes and is ready to go as well :) Thanks!