Create sample/test on ImageLoadingEstimator for TensorFlow scoring for loading an in-memory image stream (instead of files from the drive)

[CESARDELATORRE]

Related to this issue, we need a clear/simple sample code/test for ImageLoadingEstimator for TensorFlow scoring so it loads an in-memory image stream as input (instead image files from a drive).

I couldn't see a clear way to do it here (Mentioned by Gleb): https://github.com/dotnet/machinelearning/blob/master/test/Microsoft.ML.Tests/ImagesTests.cs