[ENH] Add BigBrain atlas and transformations

[justinehansen]

This PR adds a new BigBrain164k folder to the OSF repo and makes it possible to do surface transformation between the BigBrain surface, fsaverage, and fsLR. This is still a work in progress.
Checklist of things to do before merging:

• add BigBrain data to neuromaps (e.g. layer thickness? cell densities?)
• update documentation + annotation_info table
• more testing

Other things to do in the future:

• add transformations between BigBrain and CIVET surface?
• add transformations between MNI152 volume and BigBrain surface?
• update/improve BigBrain surface and medial wall mask (but this would require recomputing the BigBrain data as well)

Much of the work here was already done by the BigBrainWarp so a big shout-out to the BigBrainWarp developers and the BigBrain team (esp Claude Lepage and Lindsay Lewis) 🙏