fix: properly handle the different flavors of storage options keys

[rtyler]

This change addresses some of the problems tacked onto #2893 but does not address the concern with ECS specifically. It does however improve the handling of storage_options since the improved credential provider code was introduced

[codecov]

Codecov Report

Attention: Patch coverage is 90.69767% with 4 lines in your changes missing coverage. Please review.

Project coverage is 72.42%. Comparing base (f9436cb) to head (a55115c).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/aws/src/credentials.rs	90.69%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2931      +/-   ##
==========================================
+ Coverage   72.40%   72.42%   +0.02%     
==========================================
  Files         131      131              
  Lines       40505    40545      +40     
  Branches    40505    40545      +40     
==========================================
+ Hits        29326    29366      +40     
+ Misses       9291     9290       -1     
- Partials     1888     1889       +1     

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