[testing-on-gke part 6.5] Move code to access bucket iam role to backend

[gargnitingoogle]

Description

This change moves the logic for adding read/write permission for data buckets for the tests for the kubernetes service account, from the shell script to the python backend library. This is for being accurate for the target buckets (which should be parsed from the JSON-based workload configuration) which is not trivial in a shell script, and also for better maintainability, testability etc.

Source request: #2329 (comment) (#2359 )

This is on top of #2482 and is followed up in #2497 .

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

All modified and coverable lines are covered by tests ✅

Project coverage is 78.28%. Comparing base (327d72e) to head (967c68d).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2496      +/-   ##
==========================================
- Coverage   78.31%   78.28%   -0.04%     
==========================================
  Files         107      107              
  Lines       11770    11770              
==========================================
- Hits         9218     9214       -4     
- Misses       2069     2071       +2     
- Partials      483      485       +2     

Flag	Coverage Δ
unittests	78.28% <ø> (-0.04%)	⬇️

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[kislaykishore]

Could you add some details in the description on why this change is needed?

[gargnitingoogle]

Could you add some details in the description on why this change is needed?

Done