feat: improve DefaultObjectAccessControl: * responses

[coryan]

Just like for bucket and object access controls, we need to enrich the
responses for DefaultObjectAccessControl: *. I also made the testing
more consistent across all three resources.

Fixes #338

[codecov]

Codecov Report

Merging #346 (d3a65ff) into main (40c5f06) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #346   +/-   ##
=======================================
  Coverage   92.53%   92.54%           
=======================================
  Files          51       51           
  Lines        8056     8065    +9     
=======================================
+ Hits         7455     7464    +9     
  Misses        601      601           

Flag	Coverage Δ
unittests	92.54% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
testbench/proto2rest.py	98.90% <100.00%> (+0.03%)	⬆️
testbench/rest_server.py	98.61% <100.00%> (-0.02%)	⬇️
tests/test_proto2rest.py	97.22% <100.00%> (+0.55%)	⬆️
tests/test_testbench_bucket.py	99.09% <100.00%> (+0.03%)	⬆️

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