[Documentation] Better documentation on existing templates and data model

**Operating System**: (`Windows` or `Linux` or `MacOS`)
Windows 11

**DocFX Version Used**:
Version 2.59.0

**Template used**: (`default` or `statictoc` or contain custom template)
default

There needs to be better documentation. I'm trying to figure out how to make some changes to the templates. It is extremely hard to do without the following:

- data model passed to the render engine.
- mapping of what sections of a page correspond to what partial template when using the default theme.
- way to dump/serialize populated data model so that it can be referenced while making changes.

Since this tool was built and is used by the MS Documentation team(s), are there any internal resources (documents, training guides, etc.) that can be made public to provide better documentation/training for users of this application.

Thanks