Enable GitHub Discussions to move questions out of Issues

I might suggest enabling [GitHub Discussions](https://docs.github.com/en/discussions) page with the hope of putting all of the issues of the sort "Prophet isn't working for my dataset, please help" over there and reduce the clutter away from bugs and feature improvements. Works for me a bit over in AutoTS, although it isn't perfect. Theoretically users might answer each other's questions, although that hasn't happened too much.

It might then be worth adding a 'pinned post' to the Discussions pointing users at the hyperparameter and other pages in the Documentation (and possibly other models or other ways they can tune their forecasting).