fix(vm): read ansible-inventory host vars from the vars. annotation prefix

[fl64]

Description

d8 v ansible-inventory and the virtualization-provisioner module both build
the Ansible inventory from VM annotations, but used different keys for host
variables. This aligns the CLI with the module: host variables are read from the
vars.provisioning.virtualization.deckhouse.io/ prefix, and groups from
provisioning.virtualization.deckhouse.io/groups. Command help, usage examples
and the FAQ are updated to match.

Why do we need it, and what problem does it solve?

So that the CLI and the module treat inventory annotations the same way — the
same annotations produce the same inventory regardless of which one generates it.

What is the expected result?

Annotating a VM with
vars.provisioning.virtualization.deckhouse.io/ansible_user=cloud exposes
ansible_user as a host variable in d8 v ansible-inventory output — the same
key the module uses.

Checklist

• The code is covered by unit tests.
• e2e tests passed.
• Documentation updated according to the changes.
• Changes were tested in the Kubernetes cluster manually.

Changelog entries

section: vm
type: fix
summary: The d8 v ansible-inventory command uses the same VM annotations as the virtualization-provisioner module to set Ansible host variables.