Enable discussions on main CKAN repo and use it for Q&A and ideas

Propose enabling github discussions on the main ckan repo https://github.com/ckan/ckan/

Why?

* Could use discussions for Q&A and "i've got this issue" type stuff rather than clogging up main issue tracker
* Would provide a better (more centralized, closer to project) place for community support than, say, stackoverflow etc.
* Could use for ideas discussion and proposals (rather than having to have this separate repo here)

/cc @monikappv @amercader @anuveyatsu @jqnatividad @wardi

Check the main ckan/ckan repository settings and Discussions area, then compare them with the deprecated ckan/ideas repository notice. Done means the main repository provides Discussions for Q&A, support questions, ideas, and proposals instead of using the separate ideas tracker.

Written by the indexing model from the issue text.