📐 added: OrthogonalCollocation with gaussradau and gausslegendre schemes

[franckgaga]

The transcription method is efficient for highly stiff nonlinear systems. The default gaussradau quadrature is slightly less accurate than gausslegendre, but its an L-stable method, while the latter being A-stable.

Some comments:

1. I default to 3 collocations points per time step/interval/finite element (for a total of 4 points, if we include the point at $\tau=0$) . I found that it's a more common default (e.g. CasADi, do-mpc, Pyomo, Gekko, etc.) than 5 points (the default of SimpleColloc.jl).
2. I tried to write a concise documentation for details on the collocation and continuity constraints. The various references on this subject tend to be VERY verbose, but somehow succeed to skip important information like the differentiation matrix construction and how to use it. The preview of the documentation is available here : OrthogonalCollocation, the associated con_nonlinprogeq! method and init_orthocolloc.
3. The paper "Nonlinear modeling, estimation and predictive control in APMonitor" of Hedengren et al. (2014) mention that we should factor out the final time $\tau_{n_o}$ from the differentiation matrix, to improve the numerical robustness, but no other justifications. I don't see why at all, since the condition number of the differentiation matrix is quite low (around 50 in my test case), and the matrix is already constructed on the normalized times $\tau \in [0, 1]$. I did not do this in my implementation (similarly to SimpleColloc.jl), since it's simpler and I'm not convince that it's necessary.
4. I only support zero order hold on the manipulated inputs for now. I will add the support of first-order hold in a following release.

Closes #238

[codecov-commenter]

Codecov Report

❌ Patch coverage is 60.14760% with 108 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.54%. Comparing base (4ab5d3b) to head (7537b91).

Files with missing lines	Patch %	Lines
src/controller/transcription.jl	33.33%	106 Missing ⚠️
src/estimator/internal_model.jl	50.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #322      +/-   ##
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- Coverage   98.42%   96.54%   -1.88%     
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  Files          29       29              
  Lines        5397     5501     +104     
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- Hits         5312     5311       -1     
- Misses         85      190     +105     

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[franckgaga]

Hello @baggepinnen, I still need to implement the tests, but do you have any comments on my points above and the documentation of the new OrthogonalCollocation. The preview of the documentation is available here : OrthogonalCollocation, the associated con_nonlinprogeq! method, and init_orthocolloc.

Thanks for your time!