Address flakiness and latency in the Traffic-Based App Rewards integration test

[adetokunbo]

Fixes #6420

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[adetokunbo]

@dfordivam As discussed, I've included the switch to 1sv topology in this PR, now that TBAR bootstrap behavior is more comprehensively tested in #6392. Locally this reduces test wall clock runtime by 27%. There are other obvious stability benefits in the CI environment

[adetokunbo]

Sorry, I'll reopen with the correct branch name