Added an algorithm transfrom bst to greater sum tree (#9777)

* Added an algorithm transfrom bst to greater sum tree

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* Update and rename transform_bst_sum_tree.py to is_sum_tree.py

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Christian Clauss <cclauss@me.com>