Redesign Trajectory class to represent the planning result of Action class

# Feature Request

Rationale to move planned trajectory outside of the Action Class
- Clarify that the Action is the input and the trajectory is a output (from the perspective of planning)
- Allow a single action to have multiple planned results which can all coexist.

## Details

The class will be a redesign of the current `Trajectory` class. Probabaly renamed to `ActionPlanResult`.
It will contain the planned JointTrajectory, as well as any planning request attributes (determined by the Action Type) and statistics (supplied by the planner backend).

My plan is to have one single class that will work with all RobotMotion inhereted classes.