feat: add custom cel env support

[eddycharly]

Explanation

Add custom cel env support.

[codecov]

Codecov Report

Attention: Patch coverage is 72.72727% with 6 lines in your changes missing coverage. Please review.

Project coverage is 24.21%. Comparing base (1149afb) to head (518ec5d).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/core/compilers/cel/env.go	64.70%	2 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #541      +/-   ##
==========================================
- Coverage   24.59%   24.21%   -0.38%     
==========================================
  Files          92       92              
  Lines        4351     4369      +18     
==========================================
- Hits         1070     1058      -12     
- Misses       3171     3199      +28     
- Partials      110      112       +2     

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