Because of how Ansible local relative search paths work, the global
"files" and "templates" directories need to be next to the playbooks.
However its not intuitive to look into the playbooks directory to find
the files and templates for a host.
Therefore flatten the playbooks directory to get rid of this confusing
structure.
Also see:
https://docs.ansible.com/ansible/latest/playbook_guide/playbook_pathing.html#resolving-local-relative-paths
For now introduce node-exporter/hosts alert rules, which got taken from
https://samber.github.io/awesome-prometheus-alerts/rules
However with the labels removed from the description, since they don't
render correctly (at least in Telegram) and don't seem to provide much
value, as we render the labels in the notification anyway.
Also only have Telegram as the notification channel for now, as it was
the easiest to set up.
