Enable specifying order of channels in Pixel Extractor

[yaeldekel]

TensorFlow models can have different ordering of the channels. ML.NET currently only supports specifying channel first/last, but not the order.

[Zruty0]

Let's wait until #753 is in, then do it.

[shauheen]

@yaeldekel can you please provide more details on the solution so that someone can take this. Thanks :)

[Ivanidzo4ka]

Closed in #2602