Add API/UI option to send guest command via qemu agent

##### ISSUE TYPE
* Enhancement Request
* Feature Idea

##### COMPONENT NAME
~~~
API/UI/Backend
~~~

##### CLOUDSTACK VERSION
~~~
4.19
~~~

##### CONFIGURATION

##### OS / ENVIRONMENT

##### SUMMARY
Hi team,

I notice that actally, for vm that have qemu agent installed, is not possible through cloudstack send command to the host, like vmware guest agent tool.
This is possible with qemu agent and i notiche that `freeze` for example was implemented with this class:
https://github.com/apache/cloudstack/blob/main/plugins/hypervisors/kvm/src/main/java/org/apache/cloudstack/utils/qemu/QemuCommand.java

But is not implemented for all type of command and I don't see any API that cover it ( and also via UI I can't see any "form").

This is something that you are interested to implemet?

##### STEPS TO REPRODUCE

##### EXPECTED RESULTS

##### ACTUAL RESULTS

Commencez par plugins/hypervisors/kvm/src/main/java/org/apache/cloudstack/utils/qemu/QemuCommand.java, en particulier l’implémentation existante de freeze. Suivez la manière dont les commandes de guest-agent sont exposées via l’API et l’UI, puis définissez l’étendue des commandes prises en charge et vérifiez qu’une commande invitée peut être envoyée via les deux interfaces.

Rédigé par le modèle d'indexation à partir du texte de l'issue.