[Ballista] Introduce query stage scheduler #1934
Description
Is your feature request related to a problem or challenge? Please describe what you are trying to do.
The query stage scheduler is introduced for generating stages, maintaining the stage status changes, etc.
Describe the solution you'd like
It decouples the scheduler server and tasks. It mainly focus on maintaining the stages. With the help of future TaskSetStore, it will be much easier to maintain tasks.
Additional context