vmm: add nested option to CPU config

Add an option in the CLI to enable nested support.
Adding an option --cpu nested=on|off to the CPU
argument to enable nested support for Microsoft
Hypervisor. By default it is enabled for both KVM
and MSHV.

Signed-off-by: Muminul Islam <muislam@microsoft.com>

fuzz/fuzz_targets/http_api.rs

@@ -132,6 +132,7 @@ impl RequestHandler for StubApiRequestHandler {
                     max_phys_bits: 46,
                     affinity: None,
                     features: CpuFeatures::default(),
+                    nested: true,
                 },
                 memory: MemoryConfig {
                     size: 536_870_912,