[Python][Docs] Add architecture documentation for http-client-python emitter

[Copilot]

• Explore the http-client-python repository structure
• Understand the emitter and generator architecture
• Review existing documentation and structure
• Create comprehensive architecture documentation
• Add the documentation to the website
• Review and finalize documentation
• Fix ASCII diagram box alignment
• Add m2r transformation to emitter responsibilities
• Align directory structure comments
• Ensure all diagram right borders align at column 66
• Align all # comments to column 43 in directory tree

Original prompt

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This section details on the original issue you should resolve

<issue_title>[python] docs to introduce source code of http-client-python</issue_title>
<issue_description>Context:
http-client-python contains 2 part of code,
(1) first part is in folder "emitter" written by typescript which handle info from typespec-client-generator-code, then pass handled data to "generator/pygen" written by python to generate sdk.
(2) In pygen, it is pre-handled again in "preprocess" then pass to "codegen". In "codegen", "models" prepares all necessary info then "serializers" render files with template files of "templates" and parameter info from "models" to generated sdk file.

Ask:
With up context, write a brief introduction to "http-client-python" so that developers could understand the repo and develop quickly.

NOTE:
(1) context is just help you understand the repo but DO NOT be limited by context so you can read the files or code of this repo to make a good doc
</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [python] docs to introduce source code of http-client-python #9273

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