Run queries at a constant rate in system test deployment

[patchwork01]

Background

Split from:

• Contention system test with different operations at once #2546

Description

We'd like to be able to configure the system test deployment to be able to run queries at a constant rate in an instance of Sleeper.

This should work for either the deployAll system test, or the JUnit-based system test suite. We could just handle the deployAll system test suite and leave the JUnit-based approach for the next issue (#2709), but we need to be able to do that as a natural continuation.

Analysis

We could potentially add a scheduled lambda to the system test deployment that we can configure to submit queries to our instance. An alternative would be ECS tasks.