Adds Background operation orchestrator

What does this MR do and why?

Adds the OrchestratorWorker for Background operations.

It gets called from SchedulerWorker.

References:

• max_running_jobs is set as 10, more details can be found in this discussion.
• This is very similar to the ExecutionWorker of BBM.

Screenshots or screen recordings

Before	After

How to set up and validate locally

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Related to #578058