Refactor s3 multipart uploads (PP-1472)

[jonathangreen]

Description

Refactor multipart s3 uploads, so that the context manager is just a wrapper around logic in the main S3Service class.

Motivation and Context

In PP-1472, I need to do multipart s3 uploads outside of a context manager. The way this functionality was previously implemented this was impossible. This PR just moves the logic around so the functions are accessible outside of a context manager.

How Has This Been Tested?

• Running units tests

Checklist

• I have updated the documentation accordingly.
• All new and existing tests passed.

[codecov]

Codecov Report

Attention: Patch coverage is 94.59459% with 2 lines in your changes missing coverage. Please review.

Project coverage is 90.63%. Comparing base (f04138e) to head (bb60469).
Report is 6 commits behind head on main.

Files	Patch %	Lines
src/palace/manager/service/storage/s3.py	94.59%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1995      +/-   ##
==========================================
- Coverage   90.63%   90.63%   -0.01%     
==========================================
  Files         339      339              
  Lines       40191    40201      +10     
  Branches     8695     8695              
==========================================
+ Hits        36427    36435       +8     
- Misses       2492     2493       +1     
- Partials     1272     1273       +1     

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[tdilauro]

Looks good! 🚀