Who is the vendor of the resources needed by the project that had the highest cost of optional tip?
Highest cost of the optional tip refers to Max(total_price_including_optional_support - total_price_excluding_optional_support);
SELECT T1.vendor_name FROM resources AS T1 INNER JOIN projects AS T2 ON T1.projectid = T2.projectid ORDER BY T2.total_price_including_optional_support - T2.total_price_including_optional_support DESC LIMIT 1