Skip FOD estimation by dropping fod section

[tsalo]

Closes #362.

Changes proposed in this pull request

• Restructure init_mrtrix_csd_recon_wf to skip FOD estimation when users don't want it. It will write out all three response function files (WM, GM, CSF) even if only WM is used later.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 76.00000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 50.50%. Comparing base (38e5900) to head (317a198).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
qsirecon/workflows/recon/mrtrix.py	76.00%	2 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #398      +/-   ##
==========================================
+ Coverage   50.47%   50.50%   +0.03%     
==========================================
  Files          55       55              
  Lines        8139     8148       +9     
  Branches      944      947       +3     
==========================================
+ Hits         4108     4115       +7     
+ Misses       3792     3791       -1     
- Partials      239      242       +3     

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