(#22110) set version=0 in catalog constructor so it's always an integer (not nil)
(maint) temporarily restore json-schema to Gemfile
(#22110) add initial catalog documentation
(#22110) validate some simple catalogs against json schema
(maint) fix typo in comment and clean whitespace
(#22110) remove empty Notes section
(#22110) Documentation improvements per GH review

* Note that both POST and GET are supported with some historical
  context around the introduction of POST
* Note that the response is an example, and remove the mid-example
  comments, so that the example is cleaner
Merge pull request #1862 from kylog/issue/22110-document-catalog

(#22110) document catalog endpoint