feat: ark content generation sdk image roles example

Author: fabianlimxuhuai

volcengine-java-sdk-ark-runtime/test/java/com/volcengine/ark/runtime/ContentGenerationTaskExample.java

@@ -44,6 +44,7 @@ public static void main(String[] args) {
                 .imageUrl(CreateContentGenerationTaskRequest.ImageUrl.builder()
                         .url("${IMAGE URL HERE}")
                         .build())
+                // .role("first_frame")
                 .build());
 
         CreateContentGenerationTaskRequest createRequest = CreateContentGenerationTaskRequest.builder()