Prototype of distributed xgboost on Modin with Ray

[prutskov]

Describe the problem

Make prototype of distributed xgboost with Modin on Ray.

[prutskov]

Prototype is in progress in this fork

[prutskov]

Incorrect behavior with using parameter num_actors was detected. Issue #2401 was created.

[prutskov]

Current prototype was implemented for 3 approaches:

1. Actor per-node approach link.
2. Actor per-node with partitions locality link.
3. Actor per-core link.

Work on improving scalability in cluster is in progress.