feat(behavior_path_planner): change side shift module logic

[kyoichi-sugahara]

Description

This PR change side shift modele logic

Issue

Original logic was implemented to erase the embedded shift_line in the path when multiple lateral_offset requests came in over a short period of time.
However, there were multiple types of logics to erase shift_line and the flow was complicated.

Countermeasures

The shift_line is embedded based on the status of the ego's position along the path.
status is categorized into BEFORE_SHIFT, SHIFTING and AFTER_SHIFT.

1. Lateral offset is requested when status is BEFORE_SHIFT
   The lateral offset is updated and embbed in the shift path.

2. Lateral offset is requested when status is SHIFTING
   The lateral offset is saved and will be embbed after shifting.

3. Lateral offset is requested when status is AFTER_SHIFT
   The lateral offset is updated and embbed in the shift path.

Only one shift_line exist in a path.

document will be updated.

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[codecov]

Codecov Report

Base: 11.13% // Head: 11.11% // Decreases project coverage by -0.01% ⚠️

Coverage data is based on head (8dd7c66) compared to base (ed6b5c8).
Patch coverage: 0.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2195      +/-   ##
==========================================
- Coverage   11.13%   11.11%   -0.02%     
==========================================
  Files        1200     1200              
  Lines       86211    86303      +92     
  Branches    20802    20872      +70     
==========================================
  Hits         9596     9596              
- Misses      66482    66574      +92     
  Partials    10133    10133              

Flag	Coverage Δ		*Carryforward flag
differential	3.59% <0.00%> (?)
total	11.10% <0.00%> (ø)		Carriedforward from 53fa588

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

Impacted Files	Coverage Δ
...nner/scene_module/side_shift/side_shift_module.hpp	0.00% <ø> (ø)
.../src/scene_module/side_shift/side_shift_module.cpp	0.00% <0.00%> (ø)

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[tkimura4]

LGTM