Allowing for pinocchio backend

[pariterre]

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This change is 

[pariterre]

This PR replaces the #1051 (rebased and upgraded)

[codecov]

Codecov Report

❌ Patch coverage is 71.66213% with 104 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.26%. Comparing base (a01ed91) to head (691129a).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
bioptim/models/pinocchio/pinocchio_model.py	69.74%	95 Missing ⚠️
...ptim/examples/getting_started/example_pinocchio.py	77.41%	7 Missing ⚠️
bioptim/models/utils.py	77.77%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1055      +/-   ##
==========================================
+ Coverage   77.21%   77.26%   +0.04%     
==========================================
  Files         192      196       +4     
  Lines       21148    21508     +360     
==========================================
+ Hits        16330    16618     +288     
- Misses       4818     4890      +72     

Flag	Coverage Δ
unittests	77.26% <71.66%> (+0.04%)	⬆️

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