Stream Engine component.
Responsible for pipeline management and execution.
Stream engine has 2 executors:
1. SQL executor
2. Autonomous executor
SQL executor receives commands from user interface to quickly change some status of a pipeline.
It does not deal with stream data (Row, to be precise).
Autonomous executor deals with stream data.
Both SQL executor and autonomous executor instance run at a main thread, while autonomous executor has workers which run at different worker threads.
## Entities inside Stream Engine

## Communication between entities
Workers in AutonomousExecutor interact via EventQueue (Choreography-based Saga pattern).
