Add module to list content on proxmox storage
We first add a method to list storage content for proxmox, then use that
new methode to add an Ansible module to list content on storage attached
to a proxmox node. User can also use content filtering to define what
they want to list (backup, iso, images,...).
This commit also include the integration and unit test for that new
module.
Co-authored-by: Julian Vanden Broeck <julian.vandenbroeck@dalibo.com>
