Readthedocs build needs updating to conform with build requirements

[bartnijssen]

Two separate issues. From readthedocs:

Your project(s) "summa" don't have a configuration file. Configuration files will soon be required by projects, and will no longer be optional. Read our blog post to create one and ensure your project continues building successfully.

Your project(s) "summa" are using the deprecated "build.image" config on their ".readthedocs.yaml" file. This config is deprecated in favor of "build.os" and will be removed on October 16, 2023. Read our blog post to migrate to "build.os" and ensure your project continues building successfully.