feat: update policy command to support OCI trust policy

[JeyJeyGao]

Feat:

• add OCI trust policy support for notation policy command

Resolves #1138

[codecov]

Codecov Report

Attention: Patch coverage is 68.42105% with 12 lines in your changes missing coverage. Please review.

Project coverage is 75.99%. Comparing base (4808e08) to head (9afb873).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/notation/policy/import.go	50.00%	9 Missing and 3 partials ⚠️

❌ Your patch check has failed because the patch coverage (68.42%) is below the target coverage (80.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1173      +/-   ##
==========================================
- Coverage   76.10%   75.99%   -0.11%     
==========================================
  Files          64       64              
  Lines        3519     3529      +10     
==========================================
+ Hits         2678     2682       +4     
- Misses        646      650       +4     
- Partials      195      197       +2     

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