Ensure AWS SDK has access to object size when issuing an upload

[benoit74]

Fix #2117

data is a buffer in our usage of the S3 class, and SDK prefer buffer to streams when it comes to PubObject command, so let's simplify things.

Tested locally with forced upload to S3 (by manipulating the If-None-Match value passed to upstream get). Before the change, I have the usual warnings, after the change they are gone.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.29%. Comparing base (fc2af69) to head (150734e).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2145      +/-   ##
==========================================
- Coverage   75.33%   75.29%   -0.04%     
==========================================
  Files          41       41              
  Lines        3207     3202       -5     
  Branches      706      706              
==========================================
- Hits         2416     2411       -5     
  Misses        674      674              
  Partials      117      117              

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