callback: add support for specifying default playbook labels from Ansible configuration

[dmsimard]

What component is this about ?

The ara_default callback

What is the idea ?

Playbook labels are currently set based on the ara_playbook_labels Ansible variable: https://ara.readthedocs.io/en/latest/playbook-names-and-labels.html

In practice, this is done once at the beginning of every play here:

ara/ara/plugins/callback/ara_default.py

Lines 205 to 210 in f404247

	# Load variables to verify if there is anything relevant for ara
	play_vars = play._variable_manager.get_vars(play=play)["vars"]
	if "ara_playbook_name" in play_vars:
	self._set_playbook_name(name=play_vars["ara_playbook_name"])
	if "ara_playbook_labels" in play_vars:
	self._set_playbook_labels(labels=play_vars["ara_playbook_labels"])

It would be nice to be able to supply a default list of labels from the Ansible configuration instead of Ansible variables. This would allow labels to be applied without needing to specify Ansible variables or modify playbooks. Any labels specified as variables would be added to the default list.