[Readme update] Add image registry proxy option to E2E test configuration

[priyansh17]

Signed-off-by: Priyansh Choudhary im1706@gmail.com

This parameter was missing from readme which lets user change the container registry used to pull images. Is necessary when their clusters have policy to block unknown Container registries.

Does your change fix a particular issue?

No

Please indicate you've done the following:

• Accepted the DCO. Commits without the DCO will delay acceptance.

[priyansh17]

/kind changelog-not-required

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 60.29%. Comparing base (4e5020d) to head (f0f7b08).
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9042      +/-   ##
==========================================
- Coverage   60.30%   60.29%   -0.01%     
==========================================
  Files         378      378              
  Lines       42746    42746              
==========================================
- Hits        25777    25774       -3     
- Misses      15419    15421       +2     
- Partials     1550     1551       +1     

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