Python CodeGen should put all user configurable settings for unbranded into lib.ts for auto doc generation

[lirenhe]

Clear and concise description of the problem

This is to follow the discussion in #6299 (comment) as we are suggested to use the below command to generate documents for all user configurable settings directly from lib.ts.

../tspd/cmd/tspd.js doc . --enable-experimental --output-dir ./test

An example could be https://typespec.io/docs/emitters/json-schema/reference/emitter/

We need to ensure lib.ts contains all necessary information so that we could generate the correct spec.

Expected behavior:

When using the above command to generate the spec, it should contains

1. All configs what we expected 3rd party users to use for the emitter (some configs may come from TCGC)
2. We have detailed description for those configs.

workstream this request is associated with

This is related to the TypeSpec 1.0 GA for emitter document improvements.

Checklist

• Follow our Code of Conduct
• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.

[lirenhe]

As part of the document improvement, please ensure all client emitter should have a root node in doc site with overview page and emitter usage page which is auto-generated.
https://typespec.io/docs/emitters/clients/http-client-js/reference/

[msyyc]

#6537

[iscai-msft]

completed as part of #6537