Add tutorial for changing polynomial basis

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

Start with the existing “Changing the polynomial basis” section at the linked SumOfSquares.jl documentation page, then inspect the repository’s documentation structure to find the appropriate tutorial location. The work is done when a standalone tutorial explains this workflow clearly and is included with the project’s documentation.

Written by the indexing model from the issue text.