Janet Jackson is giving fans a little treat this Labor Day.The songstress took to Instagram on Monday to share a teaser for her upcoming two-part biographical documentary, , coming in January.The teaser features concert footage, behind-the-scenes looks at Jackson's life, old home movies, and interviews with some of her friends and contemporaries, including Mariah Carey and Paula Abdul, who remark on Jackson's impact and personality.«She's an empowered woman,» Carey says, in the teaser, as Abdul