This question has come up a lot since the webinar https://www.youtube.com/watch?v=WeBjY2OEh14 showed @abegong doing database introspection with Great Expectations.
Unfortunately, the branch Abe was working on is not a released branch and some of the calls used in the video don’t work exactly the same way on the released versions of GE. The core team knows this is a priority and will produce content to make this available, but it’s going to be several weeks before that is available.