Test Multi Process Direct Runner With Largish Data

Filing this as a tracker.

We can test multiprocess runner with a largish amount of data to the extend that we can do this on Jenkins. This will serve 2 purposes:
- Find out issues related to multi processing. It would be easier to find rare issues when running over non-trivial data.
- Serve as a baseline (if not a benchmark) to understand the limits of the multiprocess runner.

Imported from Jira [BEAM-7888](https://issues.apache.org/jira/browse/BEAM-7888). Original Jira may contain additional context.
Reported by: altay.