Adopt Nipreps configuration and maintenance docs

[tsalo]

Prepare to properly integrate ASLPrep into the Nipreps ecosystem.

I still need to figure out licensing information.

Changes proposed in this pull request

• Use config and setup structure from fMRIPrep.
• Add maintenance info from nipreps. This isn't necessarily complete, but it's a start.
• Update documentation on installation and contributing (closes Improve contributing and installation documentation #302).

[codecov-commenter]

Codecov Report

Patch coverage: 77.77% and project coverage change: -3.24 ⚠️

Comparison is base (56298bf) 66.05% compared to head (2caf563) 62.82%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #231      +/-   ##
==========================================
- Coverage   66.05%   62.82%   -3.24%     
==========================================
  Files          74       56      -18     
  Lines        6072     5103     -969     
  Branches        0      707     +707     
==========================================
- Hits         4011     3206     -805     
+ Misses       2061     1650     -411     
- Partials        0      247     +247     

Impacted Files	Coverage Δ
aslprep/utils/sentry.py	0.00% <0.00%> (ø)
aslprep/workflows/base.py	84.14% <ø> (-8.54%)	⬇️
aslprep/__about__.py	100.00% <100.00%> (ø)

... and 48 files with indirect coverage changes

☔ View full report in Codecov by Sentry.
📢 Do you have feedback about the report comment? Let us know in this issue.