[Documentation] Improve documentation for overriding attributes from vmm_exec_kvm.conf

[paczerny]

Description
There is an option to override the default configuration from vmm_exec_kvm.conf. User (admin?) can override the values in Cluster, Host and VM template. The latest has top priority.
We have a list of configuration attributes in vmm_exec_kvm.conf
But it's not clear which attributes can be overridden. Not all attributes can be defined in Cluster, Host and VM

Expected behavior
Make a list or check box to define in which object the user can override the configuration attributes.

Details

• Affected Component: Documentation
• Hypervisor: --
• Version: 6.8+

Additional context

Progress Status

• Code committed
• Testing - QA
• Documentation (Release notes - resolved issues, compatibility, known issues)