Fix Ansible lint errors (using GitLab Duo Agent Platform custom rules)

This code update modernizes an automated GitLab server setup script by making it follow current best practices. The main changes include:

1. Updated module references: All commands now use the full, official module names (like ansible.builtin.apt instead of just apt) to ensure compatibility with newer versions and avoid potential conflicts.

2. Standardized boolean values: Changed inconsistent yes/no values to the standard true/false format throughout the script, making it more reliable and consistent.

3. Minor formatting cleanup: Removed trailing whitespace and cleaned up spacing for better code readability.

4. Updated firewall module: Changed to use the community-supported firewall module instead of the basic one.

These changes don't alter what the script does - it still installs and configures GitLab on a server with all the same security settings, backups, and email configuration. However, the updates ensure the script will work reliably with current and future versions of the automation tool, reducing the risk of failures due to deprecated features or naming conflicts. It's essentially a maintenance update to keep the code current with modern standards.