Reorient data to RPI

[jcohenadad]

Data don't have the same orientation, so they need to be oriented in the same way for subsequent processing. See example:

https://github.com/sct-pipeline/ukbiobank-spinalcord-csa/blob/04b9dd20bf2ad646e734e3e3effae174d4e451ca/preprocess_data.sh#L52