Add ability to specify path constraints

[egordon]

Currently only goal constraints are considered.

Add set_path_constraint(Constraints).

Just expose the raw MoveIt2 constraint API for now. We can add helper functions later.

This allows for:

• Orientation Constraints: e.g. keep a robot link withing X degrees of level
• Position Constraints: keep a robot link within a bounded area
• Joint Constraints: e.g. prevent the planner from considering certain joint values
• Visibility Constraints: keep a link within the view frustrum of a sensor location

[egordon]

Solved in egordon/path