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Contribution guide.

Is your feature request related to a problem? Please describe.
I have been using the ADK for a while, and when configuring CORS for multi-tenant environments, I typically need to override the app object to use FastAPI’s native allow_origin_regex parameter. The current implementation of get_fast_api_app only exposes allow_origins, which is not sufficient for dynamic or pattern-based domain configurations.

Describe the solution you'd like
Include allow_origin_regex as a parameter to the get_fast_api_app, so we can send to the FastAPI object instance this allowed field.

Describe alternatives you've considered
NA

Additional context
N/A