Fix Debian 13 compatability

[fnwbr]

After trying to run this playbook on a fresh Debian 13 Trixie VM I debugged step-by-step what wasn't working. Essentially this includes two things:

1. a new way of configuring repositories using the deb822_repository module
2. a fix for Ansible 2.19 - galera_cluster_nodes is handled as string instead of list #265

Description

For 1: software-properties-common is not available for Debian 13 anymore, hence breaking the repository setup (compare https://www.reddit.com/r/debian/comments/1n9aakj/why_were_the_softwareproperties_tools_removed/ and dokku/dokku#7877 for example). This PR replaces legacy repository setup and key management with the newer deb822_repository module and removes unnecessary variables, templates, and pre-requisite packages that I assumed not to be necessary anymore.

For 2: Updates cluster node address generation in configuration templates to reference dynamic groups instead of static lists, making cluster configuration more flexible and maintainable (templates/etc/my.cnf.d/server.cnf.j2, templates/etc/my.cnf.d/server.cnf.temp.j2, templates/etc/mysql/conf.d/galera.cnf.j2, templates/etc/mysql/conf.d/galera.cnf.temp.j2)

Related Issue

Closes #265

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Chore (non-breaking change that does not add functionality or fix an issue)

Checklist:

• I have read the CONTRIBUTING document.
• I have tested this version using Debian 13 VMs

[fnwbr]

In theory this deb822 style of configuring should also work with previous versions of Debian, but I have not tested that at all. Until someone had the time to fix Molecule, maybe someone can verify my PR?

[fnwbr]

Coming from https://mariadb.org/download/?t=repo-config&d=Debian+13+%22Trixie%22; deb.mariadb.org is a dynamic mirror

[fnwbr]

Debian 13 Molecule tests were failing:

  TASK [ansible-mariadb-galera-cluster : mariadb_packages_install | installing mariadb-galera packages] ***
  fatal: [node2]: FAILED! => {"changed": false, "msg": "Failed to update apt cache: W:Updating from such a repository can't be done securely, and is therefore disabled by default., W:See apt-secure(8) manpage for repository creation and user configuration details., W:Repositories should provide a clear-signed InRelease file, but none found at https://deb.mariadb.org/10.11/debian/dists/trixie/InRelease., E:The repository 'https://deb.mariadb.org/10.11/debian trixie Release' does not have a Release file."}
  fatal: [node1]: FAILED! => {"changed": false, "msg": "Failed to update apt cache: W:Updating from such a repository can't be done securely, and is therefore disabled by default., W:See apt-secure(8) manpage for repository creation and user configuration details., W:Repositories should provide a clear-signed InRelease file, but none found at https://deb.mariadb.org/10.11/debian/dists/trixie/InRelease., E:The repository 'https://deb.mariadb.org/10.11/debian trixie Release' does not have a Release file."}

That's because for Debian 13 Trixie MariaDB's repositories only offer 12.0 or newer.
I went ahead and changed the default version to 12.0 for all setups... knowing that this might be somewhat scary. Feel free to chime in... maybe it would make more sense to only update the Molecule tests for Debian 13 to use MariaDB 12.0?