message: add date to CHANGELOG.md
diff: # CHANGELOG
  -## 0.9.0 - UNRELEASED
  +## 0.9.0 - 2022-03-29
  Requires `libfranka` >= 0.8.0
  +
  + * Added support for libfranka 0.9.0
  * **BREAKING** add base acceleration `O_ddP_O` (will for now always be {0,0,-9.81}) to `FrankaState.msg`
  * **BREAKING** add following errors to `Errors.msg`:
  * `joint_move_in_wrong_direction`
  @@ -10,7 +12,6 @@ Requires `libfranka` >= 0.8.0
  * `joint_via_motion_generator_planning_joint_limit_violation`
  * `base_acceleration_initialization_timeout`
  * `base_acceleration_invalid_reading`
  - * Added support for libfranka 0.9.0
  * `franka_gazebo`:
  - Add JointPosition and JointVelocity Interface
  - Fix: Robot now keeps position when no controller is running
  