chore: refactor bucketing key to be a pointer as all other elements from DTO

[thomaspoignant]

Description

refactor bucketing key to be a pointer as all other elements from DTO

Checklist

• I have tested this code
• I have added unit test to cover this code
• I have followed the contributing guide

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[codecov]

Codecov Report

Attention: Patch coverage is 81.81818% with 2 lines in your changes missing coverage. Please review.

Project coverage is 86.08%. Comparing base (4cbeda2) to head (3439c76).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/flag/internal_flag.go	81.81%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2395      +/-   ##
==========================================
- Coverage   86.11%   86.08%   -0.03%     
==========================================
  Files         102      102              
  Lines        3780     3787       +7     
==========================================
+ Hits         3255     3260       +5     
- Misses        400      401       +1     
- Partials      125      126       +1     

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