some settings missing from automoduleconfig output

[willkg]

Tecken has a settings file that uses the Everett configuration manager here:

https://github.com/mozilla-services/tecken/blob/cc26d300104edd3d2736a934e737b678b6dba2b6/tecken/settings.py

The docs use automoduleconfig to extract configuration documentation from that file:

https://github.com/mozilla-services/tecken/blob/cc26d300104edd3d2736a934e737b678b6dba2b6/docs/configuration.rst#L41

However, there are a lot of settings that don't make it to the configuration. For example:

• DOWNLOAD_S3_BUCKET
• DOWNLOAD_S3_REGION

In the settings.py file, those are conditionally set depending on the cloud provider value. Maybe automoduleconfig skips that?

This covers fixing automoduleconfig so it documents those variables.