Add quickest_path feature to planner

[mxgrey]

This PR adds a quickest_path feature for the planner. Asking for the quickest_path bypasses many of the normal capabilities of the planner to quickly give back an estimate of the quickest path to get between two points.

[codecov[bot]]

Codecov Report

Merging #84 (25736da) into main (7f25b26) will increase coverage by 0.06%. The diff coverage is 43.29%.

@@            Coverage Diff             @@
##             main      #84      +/-   ##
==========================================
+ Coverage   23.16%   23.23%   +0.06%     
==========================================
  Files         370      370              
  Lines       30602    30741     +139     
  Branches    14267    14362      +95     
==========================================
+ Hits         7090     7143      +53     
  Misses      14108    14108              
- Partials     9404     9490      +86     

Flag	Coverage Δ
tests	23.10% <43.29%> (+0.07%)	:arrow_up:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
..._traffic/src/rmf_traffic/agv/internal_planning.hpp	33.33% <ø> (ø)
...ffic/src/rmf_traffic/agv/planning/CacheManager.hpp	50.00% <ø> (ø)
...raffic/agv/planning/DifferentialDriveHeuristic.hpp	87.50% <ø> (ø)
...mf_traffic/agv/planning/MinimalTravelHeuristic.cpp	0.00% <0.00%> (ø)
...mf_traffic/agv/planning/MinimalTravelHeuristic.hpp	0.00% <ø> (ø)
rmf_traffic/src/rmf_traffic/agv/planning/Tree.hpp	14.28% <0.00%> (-2.39%)	:arrow_down:
rmf_traffic/test/unit/agv/test_Planner.cpp	13.64% <19.76%> (+0.29%)	:arrow_up:
...rmf_traffic/agv/planning/ShortestPathHeuristic.hpp	27.58% <33.33%> (+0.31%)	:arrow_up:
...traffic/src/rmf_traffic/agv/planning/impl_Tree.hpp	58.47% <60.00%> (-5.09%)	:arrow_down:
...raffic/agv/planning/DifferentialDriveHeuristic.cpp	57.50% <75.00%> (+0.35%)	:arrow_up:
... and 6 more