Revert file-based credential support

[reyhankoyun]

Reverts commit 362365c (PR #192).

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.14%. Comparing base (c04d410) to head (b2bb0aa).

Files with missing lines	Patch %	Lines
aws_secretsmanager_agent/src/cache_manager.rs	66.66%	0 Missing and 1 partial ⚠️
aws_secretsmanager_agent/src/config.rs	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #201      +/-   ##
==========================================
- Coverage   92.34%   92.14%   -0.21%     
==========================================
  Files          15       14       -1     
  Lines        2626     2405     -221     
  Branches     2626     2405     -221     
==========================================
- Hits         2425     2216     -209     
+ Misses        152      143       -9     
+ Partials       49       46       -3     

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[github-actions]

⚠️ Performance Alert ⚠️

Possible performance regression was detected for benchmark 'Secrets Manager Agent Benchmarks'.
Benchmark result of this commit is worse than the previous benchmark result exceeding threshold 1.50.

Benchmark suite	Current: b2bb0aa	Previous: 3db44b9	Ratio
CacheEviction	100610 ns/iter (± 16437)	59879 ns/iter (± 7240)	1.68

This comment was automatically generated by workflow using github-action-benchmark.