MAINT: Rotate CircleCI secrets and setup up org-level context

[oesteban]

Responding to CircleCI's security alert on Jan 4, 2023 this PR rotates the secrets of this project.

[codecov]

Codecov Report

Base: 98.62% // Head: 96.92% // Decreases project coverage by -1.70% ⚠️

Coverage data is based on head (8db7e81) compared to base (50dd27c).
Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #172      +/-   ##
==========================================
- Coverage   98.62%   96.92%   -1.71%     
==========================================
  Files          13       13              
  Lines        1234     1234              
  Branches      189      189              
==========================================
- Hits         1217     1196      -21     
- Misses         10       33      +23     
+ Partials        7        5       -2     

Flag	Coverage Δ
travis	96.92% <ø> (ø)
unittests	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
nitransforms/io/afni.py	80.83% <0.00%> (-17.50%)	⬇️

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