Roadmap: Improve the API Reference Generation

[chanmosq]

Summary

O3DE code base is documented using a doxygen-generated API reference. This roadmap item tracks work to improve the API reference generation tool and publish instructions on how to generate.

### Tasks
- [ ] https://github.com/o3de/sig-docs-community/issues/114
- [ ] https://github.com/o3de/o3de.org/issues/2012
- [ ] https://github.com/o3de/api.o3de.org/issues/5
- [ ] Improve the main page of each API Reference. It should not appear empty, and provide guidance or navigation for the user. (Example of a main page: [Atom Core](https://www.o3de.org/docs/api/frameworks/atomcore/))

Related Links

Link to additional information such as RFC related to the roadmap item.

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