Adding IsVMInStandbyPool boolean property in VirtualMachineInstanceView (#26069)

This change introduces a boolean property in VirtualMachineInstanceView
to indicate whether a VM is in or out of Standby Pool, which is
currently a preview feature.

Co-authored-by: Bowen Xu <box@microsoft.com>

Author: bxubxu

specification/compute/resource-manager/Microsoft.Compute/ComputeRP/stable/2023-09-01/examples/virtualMachineExamples/VirtualMachine_Get_InstanceView.json

@@ -119,6 +119,7 @@
             }
           ]
         },
+        "isVMInStandbyPool": false,
         "statuses": [
           {
             "code": "ProvisioningState/succeeded",

specification/compute/resource-manager/Microsoft.Compute/ComputeRP/stable/2023-09-01/examples/virtualMachineExamples/VirtualMachine_List_MaximumSet_Gen.json

@@ -807,7 +807,8 @@
                       "time": "2022-01-14T16:43:41.657Z"
                     }
                   ]
-                }
+                },
+                "isVMInStandbyPool": false
               },
               "licenseType": "aaaaaaaaaaaaaa",
               "extensionsTimeBudget": "aaaaaaaaaaaaaaaaaaaaaa",

specification/compute/resource-manager/Microsoft.Compute/ComputeRP/stable/2023-09-01/virtualMachine.json

@@ -3101,6 +3101,11 @@
         "patchStatus": {
           "$ref": "#/definitions/VirtualMachinePatchStatus",
           "description": "[Preview Feature] The status of virtual machine patch operations."
+        },
+        "isVMInStandbyPool": {
+          "type": "boolean",
+          "readOnly": true,
+          "description": "[Preview Feature] Specifies whether the VM is currently in or out of the Standby Pool."
         }
       },
       "description": "The instance view of a virtual machine."