Add a button to the interface to enable/disable self-collision avoidance

[hello-binit]

Stretch's ROS 2 driver recently added a service called /self_collision_avoidance of type std_srvs/SetBool, which enables programs to enable/disable self-collision avoidance on the fly. Self-collision avoidance is a safety feature where Stretch can detect and prevent self collisions between Stretch's arm and its own body.

Let's add a button to the interface which allows users to enable/disable this safety feature.