refactor(autoware_object_merger): move headers to src and rename package

[esteve]

Description

Move headers to src and rename package

Related links

Parent Issue:

• Prefix packages with autoware_ prefix and keep code in autoware namespace autoware#4569

How was this PR tested?

Notes for reviewers

None.

Interface changes

None.

Effects on system behavior

None.

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[esteve]

@technolojin I've submitted this PR as a follow-up to #7642 to update the package name and move the headers, let me know if the changes are ok. Thanks.

[technolojin]

@technolojin I've submitted this PR as a follow-up to #7642 to update the package name and move the headers, let me know if the changes are ok. Thanks.

Thank you for your work.

1. package renaming
   I forgot to explain my strategy that the package names in /perception will be changed later in a concentrated time to minimize impact of other linked repositories and systems rely on.
   However, this package name seems to be fine to be changed (considering the package name is used within autoware_universe).

2. moving headers
   I am considering the association to be shared in the future. this association part is the same as multi_object_tracker, radar_object_tracker, and tracking_object_merger.
   Let me do the re-organization later.

[esteve]

@technolojin I've moved the header files to a public directory, can you have a look at the changes when you have a moment? Thanks.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 28.91%. Comparing base (106625a) to head (948b30f).
Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7804      +/-   ##
==========================================
- Coverage   28.95%   28.91%   -0.05%     
==========================================
  Files        1606     1611       +5     
  Lines      117598   117765     +167     
  Branches    50597    50630      +33     
==========================================
  Hits        34046    34046              
- Misses      74299    74466     +167     
  Partials     9253     9253              

Flag	Coverage Δ		*Carryforward flag
differential	0.00% <ø> (?)
total	28.95% <ø> (+<0.01%)	⬆️	Carriedforward from 42e466a

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[esteve]

@yukkysaito @YoshiRi @miursh can you have a look at this PR? Thanks.

[yukkysaito]

@esteve Thank you for the reminder.
@technolojin Could you please review this?

[technolojin]

Can you fix the launcher?
$(find-pkg-share object_merger) -> $(find-pkg-share autoware_object_merger)

[technolojin]

I fixed the launchers.