Add default credentials provider

[JacksonTian]

You need to complete

• unit tests and/or feature tests
• documentation is changed or added

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 95.55556% with 2 lines in your changes missing coverage. Please review.

Project coverage is 96.45%. Comparing base (e98371f) to head (f65c223).

Files	Patch %	Lines
credentials/internal/providers/default.go	95.55%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #103      +/-   ##
==========================================
- Coverage   96.47%   96.45%   -0.02%     
==========================================
  Files          30       31       +1     
  Lines        2040     2085      +45     
==========================================
+ Hits         1968     2011      +43     
- Misses         58       59       +1     
- Partials       14       15       +1     

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