Feature request

Feature description

As discussed in the actions design doc, we should rename the goal state transitions to use active verbs.

Basically, the following event names:

can be renamed to

 GOAL_EVENT_SUCCEED, 
 GOAL_EVENT_ABORT, 
 GOAL_EVENT_CANCEL, 

Implementation considerations

This likely affects some downstream dependencies (e.g. rclcpp_action and rclpy), although it should not have a big impact since it's just renaming variables/functions.