chore(route_handler): improve warning message

[TakaHoribe]

Description

Add a warning message when the route plan is failed. Now it sometimes fails without any information nor warnings.

Tests performed

Not applicable.

Effects on system behavior

Not applicable.

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[isamu-takagi]

LGTM for mission_planner package.

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (6bf539b) 15.21% compared to head (9959678) 15.21%.

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #4252    +/-   ##
========================================
  Coverage   15.21%   15.21%            
========================================
  Files        1489     1489            
  Lines      102611   103383   +772     
  Branches    31524    32089   +565     
========================================
+ Hits        15611    15730   +119     
- Misses      70048    70575   +527     
- Partials    16952    17078   +126     

Flag	Coverage Δ		*Carryforward flag
differential	16.25% <0.00%> (?)
total	15.21% <ø> (+<0.01%)	⬆️	Carriedforward from 6bf539b

*This pull request uses carry forward flags. Click here to find out more.

Impacted Files	Coverage Δ
...ne_module/lane_change/avoidance_by_lane_change.cpp	0.00% <0.00%> (ø)
...n_planner/src/lanelet2_plugins/default_planner.cpp	22.00% <0.00%> (-0.11%)	⬇️
planning/route_handler/src/route_handler.cpp	24.80% <0.00%> (+<0.01%)	⬆️

... and 8 files with indirect coverage changes

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