Terraform example file for Proxmox Provisioner

Upgraded to work with Terraform 1.0.

- Added required providers block to work with a specific telmate version
- No need to download and compile the module now, it just downloads it from the Terraform Registry; more info here: https://registry.terraform.io/providers/Telmate/proxmox/latest/docs 
- Currently using Telmate's Proxmox Provider version 2.7.1
- There's a current issue with the interaction between Proxmox's guest agent and the Proxmox API that causes the terraform creation to last atleast 10 minutes. -> Added the `agent` entry on `0` to disable it.

Make sure you set up the variables needed to run the .tf:

- ${PROXMOX_URL}
- ${PROXMOXSUPERSECRETPASSWORD}
- ${NODETOBEDEPLOYED}
- ${SSHPERSONALPUBLICKEY}
- IP Range

Terraform 1.0 here: https://www.terraform.io/downloads.html