S3: return checksum information in MultipartUpload responses

[bpandola]

Closes #9024

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.18%. Comparing base (36fc191) to head (3701eae).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #9968   +/-   ##
=======================================
  Coverage   93.18%   93.18%           
=======================================
  Files        1321     1321           
  Lines      120327   120327           
=======================================
+ Hits       112129   112130    +1     
+ Misses       8198     8197    -1     

Flag	Coverage Δ
servertests	29.00% <0.00%> (ø)
unittests	93.16% <100.00%> (+<0.01%)	⬆️

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