docs: update migration guide to include TF2 invocation in TF1 summary APIs (#5566)
docs: update migration guide to include TF2 invocation in TF1 summary APIs (#5566)

Add instructions and example for invoking TF 2.x behaviors within TF 1.x summary API logging ops.
tensorflow/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard