feat(kubevirt_vm): add state=start/stop/restart to manage VM lifecycle

It adds support for starting, stopping, and restarting VirtualMachines.
The operations are performed through the KubeVirt restart subresource
API (PUT to `subresources.kubevirt.io/v1`). These calls are extracted
into a single shared helper function `_call_subresource()` to handle the
common flow, i.e., check mode, API call and wait conditions.
Moreover, it adds the optional parameter  `grace_period_seconds` for
stop and start operations.

Additionally, it adds unit tests and integration tests for all
operations.

Assisted-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Signed-off-by: Javier Cano Cano <jcanocan@redhat.com>

examples/play-start.yml

@@ -0,0 +1,10 @@
+---
+- name: Playbook starting a virtual machine
+  hosts: localhost
+  tasks:
+    - name: Start VM
+      kubevirt.core.kubevirt_vm:
+        state: started
+        name: testvm
+        namespace: default
+        wait: true