Relocate kafka alert schema from userguide

This MR moves the schema from the userguide to gwcelery. This allows us to easily fix a problem described both in this comment and in #486 (closed). Storing the schema here instead of the userguide allow us to sidestep problems in hop-client's automatic schema generation; if the schema are part of this repo then we can easily pass them to hop-client when sending avro messages and not rely on hop-client's automatic schema generator.

It should also be noted that although the schema have been living in the userguide's repo, the userguide itself never references them. The content page of the userguide shows manually created tables that represent the schema, but the schema are otherwise not referenced or made visible outside of the repo directory tree.