improve e2e load tests (continued)

[pgte]

Load tests need to be improved:

• [ ] make configuration accessible and documented
• [ ] run this on CI
• [ ] minimize test run time (resort to polling instead of waiting X time)
• [ ] test for data loss more thoroughly
• [ ] extract performance metrics
• [ ] impose thresholds on performance metrics

[pgte]

@jimpick could you take this one?