ENH: Chain 2-step registration for adult templates

[mgxd]

This PR alters registrations to MNI152NLin6Asym by first registering the anatomical template to MNIInfant:cohort-X, and then concatenating that transform in addition to pre-computed ones (MNIInfant:cohort-X -> MNI152NLin6Asym).

ATM, this PR fails to include the precomputed transforms, as they are quite a few (11 MNIInfant cohorts) and to/from transforms. I was originally planning on including them in nibabies, but the 3.2GB size is too much.

For the time being, the transforms are hosted at an OSF repository, until they have been finalized and structured for TemplateFlow. We use pooch to fetch the needed transform.

[codecov]

Codecov Report

Attention: Patch coverage is 39.84962% with 80 lines in your changes missing coverage. Please review.

Project coverage is 51.58%. Comparing base (8cc8db2) to head (79fc159).
Report is 8 commits behind head on master.

Files with missing lines	Patch %	Lines
nibabies/workflows/anatomical/registration.py	19.56%	37 Missing ⚠️
nibabies/workflows/anatomical/fit.py	31.37%	32 Missing and 3 partials ⚠️
nibabies/interfaces/patches.py	77.14%	6 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #415       +/-   ##
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+ Coverage   38.47%   51.58%   +13.11%     
===========================================
  Files          66       68        +2     
  Lines        6319     6595      +276     
  Branches      975      823      -152     
===========================================
+ Hits         2431     3402      +971     
+ Misses       3802     2975      -827     
- Partials       86      218      +132     

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