Add the possibility for an immersed drag

[simone-silvestri]

cc @glwagner

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 32 lines in your changes missing coverage. Please review.

Project coverage is 64.39%. Comparing base (537a555) to head (7395fb7).

Files with missing lines	Patch %	Lines
src/Rheologies/ice_stress_divergence.jl	0.00%	32 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #84      +/-   ##
==========================================
- Coverage   65.40%   64.39%   -1.01%     
==========================================
  Files          28       28              
  Lines         896      910      +14     
==========================================
  Hits          586      586              
- Misses        310      324      +14     

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[glwagner]

what does the example look like?

[simone-silvestri]

Here. The immersed drag does not seem to make much of an impact.