WIP: Scripts to plot HOG AP and RL diameters

[valosekj]

Description

This is a WIP PR, which adds scripts for plotting the AP and RL diameters calculated using the "HOG-based" approach proposed in spinalcordtoolbox/spinalcordtoolbox#4958.

How to use the PR

Get sub-unfErssm004_metrics_PAM50.csv using commands from spinalcordtoolbox/spinalcordtoolbox#4958 (comment), then run:

source ${SCT_DIR}/python/etc/profile.d/conda.sh
conda activate venv_sct
python AP_RL_diameters_PAM50.py -i sub-unfErssm004_metrics_PAM50.csv -o sub-unfErssm004_metrics_PAM50.png

example figure