Perform LABEL_DETECTION on the uploaded image

FrontendController.java

 private AnnotateImageResponse analyzeImage(String uri) {
        // After the image was written to GCS, analyze it with the GCS URI.
        // Note: It's also possible to analyze an image embedded in the
        // request as a Base64 encoded payload.
        List<AnnotateImageRequest> requests = new ArrayList<>();
        ImageSource imgSrc = ImageSource.newBuilder()
                .setGcsImageUri(uri).build();
        Image img = Image.newBuilder().setSource(imgSrc).build();
        Feature feature = Feature.newBuilder()
                .setType(Feature.Type.LABEL_DETECTION).build();
        AnnotateImageRequest request = AnnotateImageRequest
                .newBuilder()
                .addFeatures(feature).setImage(img)
                .build();

        requests.add(request);
        BatchAnnotateImagesResponse responses =
                annotatorClient.batchAnnotateImages(requests);
        // We send in one image, expecting just one response in batch
        AnnotateImageResponse response = responses.getResponses(0);

        System.out.println(response);
        return response;
    }