[Feature] isotonic regression API for practitioners

[Mamba413]

It would be interesting to give users a easy-to-use API for the isotonic regression. The regression implemented skscope is already provided in example gallery: https://skscope.readthedocs.io/en/latest/gallery/LinearModelAndVariants/isotonic-regression.html. So, this can be easily solved by wrapping the necessary code.

Reference:

• [1] Isotonic regression. https://en.wikipedia.org/wiki/Isotonic_regression

• [2] Stylianou, Mario, and Nancy Flournoy. “Dose finding using the biased coin up‐and‐down design and isotonic regression.” Biometrics 58.1 (2002): 171-177.