feat(genai): update Imagen 4 model (#13542)

Author: katiemn

genai/image_generation/imggen_with_txt.py

@@ -26,7 +26,7 @@ def generate_images(output_file: str) -> Image:
     # output_file = "output-image.png"
 
     image = client.models.generate_images(
-        model="imagen-4.0-generate-preview-06-06",
+        model="imagen-4.0-generate-001",
         prompt="A dog reading a newspaper",
         config=GenerateImagesConfig(
             image_size="2K",