Fix error code parsing for AWS S3 responses

[jotare]

Description

Error status is sometimes a number and sometimes a string with a special code. I've created a simple function to parse it and return a number always. More mappings can be added if needed

How was this PR tested?

Describe how you tested this PR.

[shortcut-integration]

This pull request has been linked to Shortcut Story #8700: Fix purge command errors.

[codecov]

Codecov Report

Attention: 8 lines in your changes are missing coverage. Please review.

Comparison is base (44a970a) 84.24% compared to head (41e6d79) 84.25%.

Files	Patch %	Lines
nucliadb_utils/nucliadb_utils/storages/s3.py	63.63%	8 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1837   +/-   ##
=======================================
  Coverage   84.24%   84.25%           
=======================================
  Files         328      328           
  Lines       18892    18908   +16     
=======================================
+ Hits        15916    15930   +14     
- Misses       2976     2978    +2     

Flag	Coverage Δ
ingest	69.88% <ø> (ø)
sdk	87.85% <ø> (ø)
utils	81.80% <65.21%> (+0.04%)	⬆️

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