feat: add IsNil to Any and AssertionTree

[eddycharly]

Explanation

Add IsNil to Any and AssertionTree.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.

Project coverage is 24.54%. Comparing base (7bc2053) to head (4a76cc4).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/apis/policy/v1alpha1/any.go	0.00%	2 Missing ⚠️
pkg/apis/policy/v1alpha1/assertion_tree.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #526      +/-   ##
==========================================
- Coverage   24.56%   24.54%   -0.03%     
==========================================
  Files          92       92              
  Lines        4344     4348       +4     
==========================================
  Hits         1067     1067              
- Misses       3167     3171       +4     
  Partials      110      110              

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