Fix memory leak issue by implementing an LRU cache for AWS credentials.

[dlorenc]

Summary

Try to fix https://github.com/sigstore/policy-controller/issues/1820

Release Note

Documentation

[codecov[bot]]

Codecov Report

:x: Patch coverage is 86.07595% with 11 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 31.17%. Comparing base (ea54b96) to head (873b812). :warning: Report is 22 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/webhook/registryauth/bounded_cache.go	91.17%	6 Missing :warning:
pkg/webhook/registryauth/registryauth.go	54.54%	4 Missing and 1 partial :warning:

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1825       +/-   ##
===========================================
- Coverage   42.78%   31.17%   -11.61%     
===========================================
  Files         121      123        +2     
  Lines        8994     9151      +157     
===========================================
- Hits         3848     2853      -995     
- Misses       4791     6065     +1274     
+ Partials      355      233      -122     

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[cpanato]

@dlorenc one lint error otherwise lgtm