DOCS: Simplified Docugami cookbook to remove code now available in docugami library (#13828)

The cookbook had some code to upload files, and wait for the processing
to finish.

This code is now moved to the `docugami` library so removing from the
cookbook to simplify.

Thanks @rlancemartin for suggesting this when working on evals.

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Co-authored-by: Taqi Jaffri <[email protected]>