Add some documentation for the templates

[edit for better description]

This adds documentation in prose for the CI templates as well as the API docs from the templates themselves. The latter are documented in the yaml file and extracted via sphinxcontrib-autoyaml. I haven't touched the existing comments yet but we should probably remove the ones that aren't directly related to a template.

The last one is unfortunate, let's home it'll get pulled quickly upstream so we don't need to pull our own repo in.