Features/292 lasso regression example

[krajsek]

Add a lasso regression example illustrating the usage of the library. The lasso regression example uses coordinate descent with soft-thresholding. Besides the HeAT version, also Numpy and PyTorch examples are provided in order to show the similarity in their implementations.

[codecov-io]

Codecov Report

Merging #307 into master will decrease coverage by 0.08%.
The diff coverage is 94.07%.

@@            Coverage Diff             @@
##           master     #307      +/-   ##
==========================================
- Coverage   96.87%   96.78%   -0.09%     
==========================================
  Files          49       53       +4     
  Lines        7875     8128     +253     
==========================================
+ Hits         7629     7867     +238     
- Misses        246      261      +15

Impacted Files	Coverage Δ
heat/ml/regression/__init__.py	100% <100%> (ø)
heat/ml/__init__.py	100% <100%> (ø)	⬆️
heat/core/dndarray.py	94.97% <100%> (+0.02%)	⬆️
heat/core/tests/test_dndarray.py	100% <100%> (ø)	⬆️
heat/ml/regression/lasso/tests/test_lasso.py	100% <100%> (ø)
heat/ml/regression/lasso/__init__.py	100% <100%> (ø)
heat/ml/regression/lasso/lasso.py	90.38% <90.38%> (ø)
... and 1 more

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[coquelin77]

this all looks good to me. but can you make the example script so someone can run it from the base directory? (as discussed previously