Fix image position when adding padding

When training and validating using batches, we currently pad the images on the four sides: top, bottom, left and right, but the img_position used during the decoding stage is wrong as it is not updated based on the position of the padding. We need to update the img_position values during images padding.

changed milestone to %DAN-P5: Improve training

added P1 label

assigned to @melodie.boillet

For now, padding have been moved to the right and bottom of the images only. The goal is to add padding on the four sides and update the image positions (used in the encoder and decoder).

Ref for 4 sides padding: f57bc667

added P2 label and removed P1 label

unassigned @mboillet

changed milestone to %DAN-P6: Training improvements Part 2

made the issue confidential

made the issue visible to everyone

changed milestone to %DAN: ML research