tctl: allow creating desktops from YAML file

To date: we have supported registering desktops in a few ways:

1. By discovering them from LDAP
2. By listing "static hosts" in the configuration file
3. Via our API
   https://github.com/gravitational/teleport/tree/master/examples/desktop-registration

This extends tctl to support creating a desktop from a YAML resource
definition, which provides an alternative for those who want more
control over the name and labels of their desktops, but don't want to
write and maintain an integration using our API.

Closes #27106

tool/tctl/common/resource_command.go

@@ -125,6 +125,7 @@ func (rc *ResourceCommand) Initialize(app *kingpin.Application, config *service.
 		types.KindDevice:                  rc.createDevice,
 		types.KindOktaImportRule:          rc.createOktaImportRule,
 		types.KindIntegration:             rc.createIntegration,
+		types.KindWindowsDesktop:          rc.createWindowsDesktop,
 	}
 	rc.config = config
 
@@ -576,6 +577,20 @@ func (rc *ResourceCommand) createNetworkRestrictions(ctx context.Context, client
 	return nil
 }
 
+func (rc *ResourceCommand) createWindowsDesktop(ctx context.Context, client auth.ClientI, raw services.UnknownResource) error {
+	wd, err := services.UnmarshalWindowsDesktop(raw.Raw)
+	if err != nil {
+		return trace.Wrap(err)
+	}
+
+	if err := client.UpsertWindowsDesktop(ctx, wd); err != nil {
+		return trace.Wrap(err)
+	}
+
+	fmt.Printf("windows desktop %q has been updated\n", wd.GetName())
+	return nil
+}
+
 func (rc *ResourceCommand) createApp(ctx context.Context, client auth.ClientI, raw services.UnknownResource) error {
 	app, err := services.UnmarshalApp(raw.Raw)
 	if err != nil {