Add tutorial for changing polynomial basis

[blegat]

We have: https://jump.dev/SumOfSquares.jl/latest/constraints/?fbclid=IwAR1LPQSwkr7viXNkAmXhyUDnSY9k0y0awFD5FukoOMEFa3_4OCBVbrPhiQ#Changing-the-polynomial-basis but also having a tutorial would be helpful.