[RTM] Added intercept for proportional states/controls

[EveCharbie]

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This change is 

[codecov]

Codecov Report

Patch coverage: 83.53% and project coverage change: +0.03 🎉

Comparison is base (f87ac04) 81.74% compared to head (9682046) 81.77%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #646      +/-   ##
==========================================
+ Coverage   81.74%   81.77%   +0.03%     
==========================================
  Files         110      111       +1     
  Lines       12429    12477      +48     
==========================================
+ Hits        10160    10203      +43     
- Misses       2269     2274       +5     

Impacted Files	Coverage Δ
bioptim/gui/check_conditioning.py	85.53% <0.00%> (ø)
...imal_control/double_pendulum_torque_driven_IOCP.py	37.06% <37.06%> (ø)
bioptim/limits/phase_transition.py	92.22% <50.00%> (ø)
...es/torque_driven_ocp/example_multi_biorbd_model.py	72.72% <72.72%> (ø)
bioptim/misc/mapping.py	89.63% <89.87%> (ø)
bioptim/optimization/optimization_variable.py	87.63% <92.85%> (ø)
bioptim/interfaces/biorbd_model.py	96.43% <96.29%> (ø)
bioptim/__init__.py	100.00% <100.00%> (ø)
bioptim/dynamics/configure_problem.py	91.22% <100.00%> (ø)
bioptim/dynamics/integrator.py	95.67% <100.00%> (ø)
... and 12 more

... and 2 files with indirect coverage changes

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[pariterre]

Test this feature?

Reviewed 1 of 1 files at r2, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @EveCharbie)

[pariterre]

Reviewed 2 of 2 files at r3, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @EveCharbie)