feat(a2a): updates advanced server customization example code to demonstrate passing additional keyword arguments to FastAPI and Starlette constructors

[snooyen]

Description

feat(a2a): updates advanced server customization example code to demonstrate passing additional keyword arguments to
FastAPI and Starlette constructors

Type of Change

• Content update/revision

Motivation and Context

• Supporting documentation for feature in feat(a2a): support passing additional keyword arguments to FastAPI and Starlette constructors sdk-python#1250 which resolves
  [FEATURE] Add support for passing keyword arguments to A2A FastAPI and Starlette constructors sdk-python#1249

Areas Affected

• Multi-agent > Agent2Agent(A2A) > Creating an A2A Server > Advanced Server Customization

Screenshots

Checklist

• I have read the CONTRIBUTING document
• My changes follow the project's documentation style
• I have tested the documentation locally using mkdocs serve
• Links in the documentation are valid and working
• Images/diagrams are properly sized and formatted
• All new and existing tests pass

Additional Notes

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terms of your choice.