DNR: Add functional tests for Session Persistence OSS and Plus

[salonichf5]

Proposed changes

Write a clear and concise description that helps reviewers understand the purpose and impact of your changes. Use the
following format:

Problem: We want to ensure everything works as expected for Session persistence feature

Solution: Add functional tests for Session persistence

Did some code refactoring for request and response, verified all tests pass

Note : need to check if ubi builds pass with experimental mode always on, or else need to fix this test

Testing: Ran tests locally

Please focus on (optional): If you any specific areas where you would like reviewers to focus their attention or provide
specific feedback, add them here.

Closes #4232

Checklist

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• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

Release notes

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please add a brief note that summarizes the change.

NONE

[tataruty]

oh, thank you! this PR helps me a lot with ProxySettings functional tests!