Add Speed Limit Requests

[PranayShirodkar]

Changes

continuous_checker

• Add continuous_checker param to LaneBlocker node. This param is a bool with default value false.
• If obstacles are static, continuous_checker should be left as false. If obstacles are dynamic/moving, set continuous_checker to true.
• When continuous_checker is false, the LaneBlocker node will only check an obstacle for intersection with all lanes when the obstacle first appears.
• When continuous_checker is true, the LaneBlocker node will continuously check an obstacle for intersection with all lanes as long as the obstacle is present.

add speed limits

• Lanes can now be in Closed state, Speed Limited state and normal state
• Refactored the lane open and lane close msg creation and sending
• Add speed limit and speed unlimit msg
• Handle all 6 possible state transitions
• Add python bindings for agv::FleetUpdateHandle::limit_lane_speeds() and agv::FleetUpdateHandle::remove_speed_limits() - related PR in rmf_demos

[mxgrey]

@Yadunund since this is targeting your draft PR #210 I'll leave it up to you if/when/how this gets merged.

[Yadunund]

I've left TODOs for things to address before merging into main. Fixed const correctness and made an API tweak to the publisher functions to prevent segfaults if the unordered_maps containing the unique_ptrs are accessed after moving the messaging during publish().