Manhattan-based eyewear company Warby Parker will open its third Brooklyn location on Jan. 25.   The new Park Slope outpost, located at 208 Flatbush Ave. between Dean and Bergen streets, follows the opening of a Williamsburg location in 2019 and a Boerum Hill storefront marked the company’s first venture into the borough in 2016.  “Brooklyn is home to so many designers, entrepreneurs, and artists cultivating an incredibly supportive community,” says co-founder and co-CEO Dave Gilboa. “Naturally…