refactor: move assertion package in core

[eddycharly]

Explanation

Move assertion package in core.

[codecov]

Codecov Report

Attention: Patch coverage is 54.54545% with 10 lines in your changes missing coverage. Please review.

Project coverage is 23.39%. Comparing base (7917252) to head (a3fa374).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/apis/policy/v1alpha1/assertion_tree.go	0.00%	5 Missing ⚠️
pkg/core/assertion/assertion.go	44.44%	4 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #497      +/-   ##
==========================================
+ Coverage   23.08%   23.39%   +0.30%     
==========================================
  Files          88       87       -1     
  Lines        4102     4100       -2     
==========================================
+ Hits          947      959      +12     
+ Misses       3070     3053      -17     
- Partials       85       88       +3     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.