Incorporate custom credential loader for refreshing storage credentials

[vustef]

Implements a custom credentials loader that loads credentials using REST catalog. Then pass that credential loader to the catalog itself so that it can be used to refresh credentials.

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 60.00000% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.63%. Comparing base (2e0149c) to head (c39f7b0).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
src/catalog.jl	60.00%	4 Missing ⚠️
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Additional details and impacted files

@@            Coverage Diff             @@
##             main      #54      +/-   ##
==========================================
- Coverage   87.01%   86.63%   -0.38%     
==========================================
  Files           9        9              
  Lines         670      681      +11     
==========================================
+ Hits          583      590       +7     
- Misses         87       91       +4     

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