code: @Override
      public ListFacesResult listFaces(ListFacesRequest request) {
          request = beforeClientExecution(request);
          return executeListFaces(request);
      }
docs: <p>
  Returns metadata for faces in the specified collection. This metadata includes information such as the bounding
  box coordinates, the confidence (that the bounding box contains a face), and face ID. For an example, see Listing
  Faces in a Collection in the Amazon Rekognition Developer Guide.
  </p>
  <p>
  This operation requires permissions to perform the <code>rekognition:ListFaces</code> action.
  </p>
  
  @param listFacesRequest
  @return Result of the ListFaces operation returned by the service.
  @throws InvalidParameterException
  Input parameter violated a constraint. Validate your parameter before calling the API operation again.
  @throws AccessDeniedException
  You are not authorized to perform the action.
  @throws InternalServerErrorException
  Amazon Rekognition experienced a service issue. Try your call again.
  @throws ThrottlingException
  Amazon Rekognition is temporarily unable to process the request. Try your call again.
  @throws ProvisionedThroughputExceededException
  The number of requests exceeded your throughput limit. If you want to increase this limit, contact Amazon
  Rekognition.
  @throws InvalidPaginationTokenException
  Pagination token in the request is not valid.
  @throws ResourceNotFoundException
  The collection specified in the request cannot be found.
  @sample AmazonRekognition.ListFaces