anterior-posterior subdivisions option

[akhanf]

Add a rule and CLI option for performing dynamic subdivision of the atlas into A-P subdivisions.

Values could be '1', 'hbt', 'uhbt' or '#' (any number), where hbt/uhbt will result in a custom subdivision based on applying the consensus HSG protocol on bigbrain (or any other templates/datasets that make sense).

Have some principled way to assigning numeric labels - then also need to create the corresponding LUT dynamically.

The text labels for each, for hbt/uhbt it's obvious - but for custom # of subdivisions.
One option, is we append _AP#of# (CA1_AP1of4, Sub_AP1of4) (todo: add in full example lut for clarity)

Labels that don't overlap with the coordinates (e.g. SRLM, Cyst) need to be excluded from this. Have a list of these to exclude, maybe in the atlas config section.

(Discussed in June 4 2024 Hippo Meeting)