Update locust script to allow tests that work on long chains of transactions with the same contact

[exalate-issue-sync]

While working on https://fecgov.atlassian.net/browse/FECFILE-2726, Dan had to modify the locust tests to ensure they were testing the scenarios where we were updating long transaction chains. Diff here.

Come up with an edit to the locust scripts that lets us run them in this manner while still allowing us to run them in the way we are now

QA Notes

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DEV Notes

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Design

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See full ticket and images here: FECFILE-2913