Add progress to MoveGroupSequence Feedback

[rr-tom-noble]

Is your feature request related to a problem? Please describe. When planning a sequence of poses, it would be useful to receive information about the number of points planned in the feedback. This allows for measuring the progress of the plan and estimations of the time left to complete.

Describe the solution you'd like I can think of a few options that could be added to the Feedback portion of the action:

• The number of planned points and total number of points
• Just the number of planned points (expect user to fetch total points from e.g. the request)
• The percentage (or fractional equivalent) of planned points

Describe alternatives you've considered Previously, we moved away from using the GetMotionSequence to performing the bulk of the logic ourselves so we could have more oversight into the process, however, this proved very slow as it required making a call to MoveGroupInterface::plan() i.e. calling the MoveGroup action for each point.

Additional context Happy to have a go at implementing this myself