Ten years ago, Bristol Palin became the world’s most famous teen mother. Now, she’s joined the cast of Teen Mom OG (premiering Oct. 1 on MTV) and is ready to tell her side of the story. “No matter what I’m doing, there’s always going to be people talking,” Palin, 27, tells Us. “If I can sit here and be some sort of light at the end of the tunnel — whether it’s being married to someone with PTSD, or going through a divorce, or trying to juggle single parenthood, then that’s what I need to do.” A mom to son, Tripp, 9 (with Levi Johnston, 28), and daughters, Sailor, 2, and Atlee, 17 months, with her ex-husband, Marine Dakota Meyer, 30, Palin admits she’s looking forward to bonding with fellow…