refactor OIDMatcher into separate utils package

[linus-sun]

Summary

This PR refactors the OIDMatcher type into a separate utils package, which will subsequently enable this PR to refactor the renderFulcioOIDMatchers function into a struct method (re: discussion here).

Release Note

NONE

Documentation

NONE- related documentation changes will happen in their respective PRs.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 58.29%. Comparing base (d271ec7) to head (8504b2f).
Report is 100 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #454      +/-   ##
==========================================
- Coverage   64.02%   58.29%   -5.73%     
==========================================
  Files           4        7       +3     
  Lines         303      458     +155     
==========================================
+ Hits          194      267      +73     
- Misses         78      149      +71     
- Partials       31       42      +11     

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[mihaimaruseac]

This looks good, but question on pkg/util/file/file.go and pkg/util/file/file_test.go as they seem unrelated: do we want them in this PR?

[linus-sun]

This looks good, but question on pkg/util/file/file.go and pkg/util/file/file_test.go as they seem unrelated: do we want them in this PR?

I believe they're referenced because I moved them out of the pkg/util folder itself into a separate pkg/util/file folder so I can also put identity_utils in its own util subfolder, otherwise I'd have to put identity_utils in the file package, which doesn't seem suitable

[linus-sun]

Just realized this duplicates the file utils, should be fixed