Run 'backup' task only when backup tag is specified

[giem-git]

A number of config tasks in tdp_collection have a backup task, generally like this :

name: Backup configuration
ansible.builtin.copy:
    src: "{{ conf_dir }}/"
    dest: "{{ conf_dir }}.{{ ansible_date_time.epoch }}"
    remote_src: true
tags:
  - backup

This has two unwanted side effects :

• make the playbook non idempotent (above backup task will be considered as changed)
• clutter conf_dir parent directory (generaly /etc/) with copied backup directories.

This step should be run only when the backup tag is specified on the command line.
Proposed resolution would be to add the never special tag as specified in ansible documentation to all backup tasks