Relocate kafka alert schema

This MR removes the kafka alert schema from the userguide. It's not actually used anywhere in the userguide except in a few unit tests, and storing it in gwcelery would solve technical problems described in gwcelery!1122 (closed).

Note that the CI pipeline for this MR will not succeed until the schema is stored elsewherehave been checked into the main branch on gwcelery. I'll remove draft from the title once it's on main and the ci pipeline for this branch succeeds.

Mar 27, 2023 Edit: We're going to move the schema to their own package.