Add E2E test for parallel files upload and download

[qiuming-best]

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Does your change fix a particular issue?

Fixes #7694

Please indicate you've done the following:

• [ ] Accepted the DCO. Commits without the DCO will delay acceptance.
• [ ] Created a changelog file or added /kind changelog-not-required as a comment on this pull request.
• [ ] Updated the corresponding documentation in site/content/docs/main.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 58.66%. Comparing base (a798182) to head (a628cb5). Report is 12 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #7691 +/- ## ======================================= Coverage 58.66% 58.66% ======================================= Files 344 344 Lines 28723 28731 +8 ======================================= + Hits 16849 16854 +5 - Misses 10445 10448 +3 Partials 1429 1429 ```

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