refactor(raindrop_cluster_filter)!: fix namespace and directory structure

[technolojin]

Description

This PR puts headers in the autoware namespace.

Additional works

1. Align directory structure to follow the coding guidelines.

Related links

Part of: autowarefoundation/autoware#4569

How was this PR tested?

Tested in a local recompute environment and the TIER IV Cloud environment.
TIER IV INTERNAL

Notes for reviewers

None.

Interface changes

None.

Effects on system behavior

None.

[github-actions]

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[yukkysaito]

LGTM

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 0.00%. Comparing base (3d849e9) to head (4522419).
Report is 586 commits behind head on main.

Files	Patch %	Lines
...r_filter/src/low_intensity_cluster_filter_node.cpp	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #7785       +/-   ##
==========================================
- Coverage   15.09%   0.00%   -15.10%     
==========================================
  Files        1967      85     -1882     
  Lines      135941    4175   -131766     
  Branches    42122     315    -41807     
==========================================
- Hits        20520       0    -20520     
+ Misses      92700    4175    -88525     
+ Partials    22721       0    -22721     

Flag	Coverage Δ
differential	0.00% <0.00%> (?)
total	?

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