Sen. Elizabeth Warren, D-Mass., was grilled on CNBC over Vice President Kamala Harris' plan to impose federal price controls on food and groceries in a nearly 20-minute-long debate on "Squawk Box" on Friday.Harris announced last week that if elected, her administration would impose federal controls on the price of food and groceries to keep corporations from exploiting consumers. The plan has received widespread criticism from economists on the left and right, who argue that artificial controls have been tried in communist countries and they do not work; in fact, they may actually increase prices for consumers, critics say.CNBC host Joe