Investigative-minded Brooklynites are searching for a delivery worker captured in a viral video wading through waist-deep flood water while delivering grub in Williamsburg during Wednesday night’s torrential downpour — hoping to give the hard-working hero a hefty $1,700 tip.  Johnny Miller shared the harrowing video on his Twitter account @UnequalScenes after he saw the delivery man’s extraordinary effort to push his e-bike through the water at Roebling and N. 11th streets just after 10 pm. And through it all! @Grubhub delivery still out there bringing your dinner #ida #flooding #brooklyn pic.twitter.com/2baP69JXhW — …