Add Configuration Schema (#3696)

* Add Configuration Schema

This adds type and description information to the configuration using
the jsonschema spec.

So far this is only a proof of concept, and touches only a couple of
entries.

* Add schema test to CI

* Try using sphinx-jsonschema

* Add more configuration descriptions

* add more descriptions

* add a bunch more descriptions

* use multi-line text blocks

* add more descriptions

* Test completeness of schema

* add new config value

* Revert changes adding a docpage

* Add informative error when config and schema are out of sync