[testing-on-gke part 1.2] Support generic workloads in gke load test-run scripts

[gargnitingoogle]

Description

This adds on top of #2247, #2284 and #2264 .

This is followed up in #2270 .

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 78.70%. Comparing base (14e7813) to head (ed2ee46).
Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2268      +/-   ##
==========================================
- Coverage   79.10%   78.70%   -0.40%     
==========================================
  Files         105      105              
  Lines       11620    11690      +70     
==========================================
+ Hits         9192     9201       +9     
- Misses       1968     2029      +61     
  Partials      460      460              

Flag	Coverage Δ
unittests	78.70% <ø> (-0.40%)	⬇️

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