[FEATURE] Add a proxmox_virtual_environment_vm datasource

[Zempashi]

Is your feature request related to a problem? Please describe.
Provider return ```Error: Received an HTTP 500 response - Reason: unable to find configuration file for VM 9000 on node 'pve-03', because I omitted the node_name during clone (I provided just `vm_id`: 9000 not located on the node I want to put my VM)

Describe the solution you'd like
A datasource proxmox_virtual_environment_vm would be nice to find a VM by it's id or by it's name, so we can found node_name and vm_id we can pass later to clone subresource.

Describe alternatives you've considered
Other possibility like the telmate/terraform-provider-proxmox, would be to support clone by it's name directly, but I like the philosophy of this provider where resource are clear and no magic happens, so I found datasource would offer more use cases...

[Anguianolabs]

This project has died.

[dmeulen]

Yup, such a pity IMHO this provider is much better than the telemate provider. Don't know what happened here, all danitso's projects are suddenly flatlined ( hope the guy is still alive and kicking ). But the bpg fork seems to implemt some fixes...

[danitso-dp]

The project is on hiatus ;-)

No. Jokes aside, I've been busy with life and my full time job. I simply haven't had time to continue my work on this project. I haven't abandoned it but it's hard to find the time for it right now. Hopefully, that'll change.