Reducing list API payload

[anushka567]

Description

Fetching only selected attributes using query.SetAttrSelection for ListObjects API which are sufficient for serving the request and reduce the payload for network call.
Reduction in payload : ~75%
Reduction in latency : ~8.5%
Also included : necessary changes in the fake bucket tests.

Perf Metrics for listing :

Test Directory Size ( in number of files)	Mean Latency(Master) (in msec)	Mean Latency(reduced payload) (in msec)	Percentage Improvement
1000	61.153	56.325	7.89%
10000	462.775	410.701	11.25%
50000	2373.293	2103.235	11.38%
100000	4677.908	4354.92	6.90%
200000	9417.683	8628.266	8.38%

Note: More detailed metrics here

Link to the issue in case of a bug fix.

NA

Testing details

1. Manual - NA
2. Unit tests - NA
3. Integration tests - NA

[codecov]

Codecov Report

Attention: Patch coverage is 94.73684% with 4 lines in your changes missing coverage. Please review.

Project coverage is 77.49%. Comparing base (ede87e1) to head (f25156b).
Report is 7 commits behind head on master.

Files with missing lines	Patch %	Lines
internal/storage/bucket_handle.go	20.00%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2627      +/-   ##
==========================================
- Coverage   77.56%   77.49%   -0.07%     
==========================================
  Files         109      109              
  Lines       15576    15603      +27     
==========================================
+ Hits        12081    12092      +11     
- Misses       2979     2992      +13     
- Partials      516      519       +3     

Flag	Coverage Δ
unittests	77.49% <94.73%> (-0.07%)	⬇️

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