Add template and VM schemas about terraform-provider-opennebula

[treywelsh]

The UserTemplate part is managed through the tags schema for now :)
In fact, the tags schema was added to manage custom key, value pairs (So tags may manage a subset of the UserTemplate part in the future).
However, there is a limitation, only key, value pairs are managed, not custom vectors.

[trenton42]

I'm not sure if I missed it, but I think the User Template section is also missing on VMs

[trenton42]

Thank you! That is helpful 👍

[perrfect]

Hello.
How correctly use USER_INPUTS?
I do:

  user_inputs = {
    ROLE = "M|text|ANSIBLE_ROLE| |"
  }

But I've got an error:
Blocks of type "user_inputs" are not expected here.

[treywelsh]

The user inputs part is not managed by the provider for now, but PR #154 will enable it