Support configurable segment balancer strategy

Currently pinot doesn't consider disk usage ratio when distribute segments and cause high skewed issue.

Refer to Druid, which can support configurable segment balancer.

https://druid.apache.org/docs/latest/configuration/index.html

druid.coordinator.balancer.strategy

Start with the issue description and the linked Druid balancer configuration, especially druid.coordinator.balancer.strategy. Define how Pinot should make segment balancing configurable and account for disk usage ratio; done should include a documented strategy and validation that balancing reduces skew.

Written by the indexing model from the issue text.