## What changed?
Include backlog counts (quanitzed) in partition scale state and info,
and use
them in simple scaler.
## Why?
Scaling based on large backlogs, and later load balancing based on
backlog too.
## How did you test it?
- [ ] built
- [ ] run locally and tested manually
- [ ] covered by existing tests
- [x] added new unit test(s)
- [x] added new functional test(s)