UPdate PCL with whole mouse brain taxonomy

[dosumis]

• Make BDSO style repo for WMB in PCL.
• Source brain region mappings from MerFish data for WMB in PCL
  • Can be extracted from paper https://static-content.springer.com/esm/art%3A10.1038%2Fs41586-023-06812-z/MediaObjects/41586_2023_6812_MOESM8_ESM.xlsx - but need to check if there are more recent mappings we can use.
• Make plan for how to use taxonomy as input
• Review and update textual definition design patterns.
• Review 'root' node strategy - update if needed.
• @scheuerm & colleagues to provide NS-Forest markers for WMB in PCL #61

Precendents:

https://github.com/Cellular-Semantics/whole_human_brain_ontology - can be used as starting point for design.
Note - for reference only- we have an earlier attempt at buiding a WMB cell type ontology based on the preprint https://github.com/Cellular-Semantics/whole_mouse_brain_ontology.