Refactor: introducing group/community.general.proxmox module defaults group

Ansible 2.12 (?) introduced Module defaults groups or action_groups, and there is a group/community.general.proxmox such group for proxmox modules.

Presently, for each task, we use execute either a password authentication task, either a token one, and we use module_defaults to factorize the long list of arguments lists.

We could revert the logic: choose either password or token authentication and set them as module_defaults, and then call to all the logic with this factorized authentication mode.