add has duplicate method

[Diogenesoftoronto]

HasDuplicate is a method identical in function to the one in legacy enduro here. This is the first part in a series of PRs to close issue #851

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 9 lines in your changes are missing coverage. Please review.

Project coverage is 48.62%. Comparing base (6b6cdf8) to head (8feff70).
Report is 5 commits behind head on main.

Files	Patch %	Lines
internal/package_/package_.go	0.00%	7 Missing ⚠️
internal/package_/goa.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #913      +/-   ##
==========================================
+ Coverage   48.13%   48.62%   +0.48%     
==========================================
  Files         103      103              
  Lines        5555     5582      +27     
==========================================
+ Hits         2674     2714      +40     
+ Misses       2637     2620      -17     
- Partials      244      248       +4     

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[jraddaoui]

I'll close this PR since we are now using Ent in the package service.