feat: Add proxying support for images (#2427)

- Closes #2418

tests/components-lib/media-player/updating-image.test.ts

@@ -144,7 +144,7 @@ describe('UpdatingImageMediaPlayerController', () => {
     it('should return screenshot URL with cached value controller', async () => {
       const url = 'data:image/png;base64,';
       const cachedValueController = mock<CachedValueController<string>>();
-      Object.defineProperty(cachedValueController, 'value', { value: url });
+      cachedValueController.getValue.mockReturnValue(url);
 
       const controller = new UpdatingImageMediaPlayerController(
         createLitElement(),