Add hook to update and read argv before parsing

[pvandyken]

None of our current plugins use it, but this will be helpful for apps that need to do extra processing on their CLI arguments beyond what can be handled by the bidsapp architecture.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.50%. Comparing base (f9c43db) to head (19737c0).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #417      +/-   ##
==========================================
+ Coverage   94.49%   94.50%   +0.01%     
==========================================
  Files          55       55              
  Lines        2180     2184       +4     
==========================================
+ Hits         2060     2064       +4     
  Misses        120      120              

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