NEW YORK — Dan Rather returned to the CBS News airwaves for the first time since his bitter exit 18 years ago, appearing in a reflective interview on “CBS Sunday Morning” days before the debut of a Netflix documentary on the 92-year-old newsman’s life. After 44 years at the network, 24 as anchor of the “CBS Evening News,” Rather left under a cloud following a botched investigation into then-President George W. Bush’s military record. Rather signed off as anchor for the last time on March 9, 2005, and exited the network when his contract ended 15 months later.