Brian Steinberg Senior TV EditorPublicis Media said it would launch a “multi-year” effort aimed at getting advertisers to invest more regularly in media outlets that cater to people from a broader range of cultures and background, part of a growing effort by Madison Avenue to rectify years of focusing mainly on mainstream media as vehicles for the majority of clients’ advertising.Publicis, the media-buying arm of Publicis Groupe of France, said it had launched the Once & For All Coalition, a