feat: fixed doc string comment mismatch in Product Search (#4432)

Changes documentation string for a GCS example from `file_path` to `image_uri`.

vision/cloud-client/product_search/product_search.py

@@ -107,7 +107,7 @@ def get_similar_products_uri(
         location: A compute region name.
         product_set_id: Id of the product set.
         product_category: Category of the product.
-        file_path: Local file path of the image to be searched.
+        image_uri: Cloud Storage location of image to be searched.
         filter: Condition to be applied on the labels.
         Example for filter: (color = red OR color = blue) AND style = kids
         It will search on all products with the following labels: