SchemaV2: Fix saving of transparent setting of vizPanel (#104443)

* save transparent setting

* make sure we test both transparent and non transparent

public/app/features/dashboard-scene/serialization/__snapshots__/transformSceneToSaveModelSchemaV2.test.ts.snap

@@ -71,6 +71,7 @@ exports[`transformSceneToSaveModelSchemaV2 should transform scene to save model
           },
         ],
         "title": "Test Panel",
+        "transparent": true,
         "vizConfig": {
           "kind": "timeseries",
           "spec": {

public/app/features/dashboard-scene/serialization/transformSceneToSaveModelSchemaV2.test.ts

@@ -268,7 +268,6 @@ describe('transformSceneToSaveModelSchemaV2', () => {
                     title: 'Test Panel 2',
                     description: 'Test Description 2',
                     fieldConfig: { defaults: {}, overrides: [] },
-                    displayMode: 'transparent',
                     pluginVersion: '7.0.0',
                     $timeRange: new SceneTimeRange({
                       timeZone: 'UTC',

public/app/features/dashboard-scene/serialization/transformSceneToSaveModelSchemaV2.ts

@@ -220,6 +220,7 @@ export function vizPanelToSchemaV2(
       title: vizPanel.state.title,
       description: vizPanel.state.description ?? '',
       links: getPanelLinks(vizPanel),
+      transparent: vizPanel.state.displayMode === 'transparent' ? true : undefined,
       data: {
         kind: 'QueryGroup',
         spec: {