Enable using short-lived credentials in Local mode (#403)

[humanzz]

Issue #, if available: #403

*Description of changes: Enable using short lived credentials in local mode

Merge Checklist

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• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works (if appropriate)
• I have updated the changelog with a description of my changes (if appropriate)
• I have updated any necessary documentation (if appropriate)

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[codecov-io]

Codecov Report

Merging #418 into master will increase coverage by 0.07%.
The diff coverage is 93.33%.

@@            Coverage Diff             @@
##           master     #418      +/-   ##
==========================================
+ Coverage   93.36%   93.44%   +0.07%     
==========================================
  Files          53       53              
  Lines        3724     3737      +13     
==========================================
+ Hits         3477     3492      +15     
+ Misses        247      245       -2

Impacted Files	Coverage Δ
src/sagemaker/local/image.py	88.53% <93.33%> (+1.03%)	⬆️

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[iquintero]

Thanks for submitting this. It looks great.