kola/azure: set default VM size to Standard_D2_v3

The default size of Standard_D2_v2 does not support Hyper-V Gen2 VMs.
Now that we are only producing Gen2[1], update the default to
Standard_D2_v3, which does support Gen2 VMs.

[1]: coreos#4109

Author: marmijo

docs/kola.md

@@ -247,8 +247,8 @@ In order to see the logs for these tests you must enter the `tmp/kola/name_of_th
 - `gcp-json-key` is using a service account's JSON key for authentication, how to create service account keys refer to https://github.com/coreos/coreos-assembler/blob/main/docs/mantle/credentials.md#gcp.
 - `gcp-project` is meant for testing in the specified project, or it will use the same as `<GCP Image Project>`.
 
-`cosa kola run --arch=x86_64 -p=azure --azure-credentials azureCreds.json --azure-disk-uri ${ImageId} basic` This will run the basic tests on Azure using default machine type `Standard_D2_v2`.
+`cosa kola run --arch=x86_64 -p=azure --azure-credentials azureCreds.json --azure-disk-uri ${ImageId} basic` This will run the basic tests on Azure using default machine type `Standard_D2_v3`.
 - `azure-credentials` is a JSON file generated by hand to pass authentication to our mantle code that will then use it to authenticate with azure services, how to create credentials refer to https://github.com/coreos/coreos-assembler/blob/main/docs/mantle/credentials.md#azure
 - `azure-disk-uri` is Azure disk uri of the custom image, this could be a gallery image version if you are using Azure Compute Gallery, refer to https://learn.microsoft.com/en-us/azure/virtual-machines/azure-compute-gallery. For example, get gallery image id via command: `galleryImageId=$(az sig image-version show --gallery-image-definition "${gallery_image_definition}" --gallery-image-version "${gallery_image_version}" --gallery-name "${gallery_name}" --resource-group $az_resource_group | jq -r .id)`.
 - `azure-location` specifies Azure location if you want to use custom location, by default is `westus`.
-- `azure-size` specifies Azure machine size if you want to use custom size, by default is `Standard_D2_v2`.
+- `azure-size` specifies Azure machine size if you want to use custom size, by default is `Standard_D2_v3`.

mantle/cmd/kola/options.go

@@ -99,7 +99,7 @@ func init() {
 	sv(&kola.AzureOptions.Sku, "azure-sku", "alpha", "Azure image sku/channel (default \"alpha\"")
 	sv(&kola.AzureOptions.Version, "azure-version", "", "Azure image version")
 	sv(&kola.AzureOptions.Location, "azure-location", "westus", "Azure location (default \"westus\"")
-	sv(&kola.AzureOptions.Size, "azure-size", "Standard_D2_v2", "Azure machine size (default \"Standard_D2_v2\")")
+	sv(&kola.AzureOptions.Size, "azure-size", "Standard_D2_v3", "Azure machine size (default \"Standard_D2_v3\")")
 	sv(&kola.AzureOptions.AvailabilityZone, "azure-availability-zone", "1", "Azure Availability Zone (default \"1\")")
 
 	// do-specific options