private ApiFuture<GenerateContentResponse> generateContentAsync(GenerateContentRequest request)
      throws IOException {
    return vertexAi.getPredictionServiceClient().generateContentCallable().futureCall(request);
  }
A base generateContentAsync method that will be used internally.

@param request a {@link com.google.cloud.vertexai.api.GenerateContentRequest} instance
@return a {@link com.google.api.core.ApiFuture} represents the response of an asynchronous
    generateContent request
@throws IOException if an I/O error occurs while making the API call
java-vertexai/google-cloud-vertexai/src/main/java/com/google/cloud/vertexai/generativeai/GenerativeModel.java