[backend] Refactor aws sdk to use the standard approach of the readme

[richard-julien]

Try to align the way to log in with IAM following the README.

We need to find a way to test that in AWS.

[codecov]

Codecov Report

Attention: 7 lines in your changes are missing coverage. Please review.

Comparison is base (8d9fb1b) 64.82% compared to head (9673df1) 64.81%.
Report is 1 commits behind head on master.

❗ Current head 9673df1 differs from pull request most recent head 0091fa3. Consider uploading reports for the commit 0091fa3 to get more accurate results

Files	Patch %	Lines
...tform/opencti-graphql/src/database/file-storage.js	46.15%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5791      +/-   ##
==========================================
- Coverage   64.82%   64.81%   -0.02%     
==========================================
  Files         521      521              
  Lines       61359    61347      -12     
  Branches     4903     4900       -3     
==========================================
- Hits        39778    39762      -16     
- Misses      21581    21585       +4     

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