docs: Change CORS headers example to use array syntax (#11243)

* docs: Change CORS headers example to use array syntax

This ensures that the LANGFLOW_CORS_* environment variable examples are using the correct and working syntax.

* Place origins in list[str] as well

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Co-authored-by: Jordan Frazier <jordan.frazier@datastax.com>
Co-authored-by: Jordan Frazier <122494242+jordanrfrazier@users.noreply.github.com>