Automatic merge from submit-queue (batch tested with PRs 39898, 39904)

[scheduler] interface for config

**What this PR fixes**

This PR converts the Scheduler configuration factory into an interface, so that
- the scheduler_perf and scheduler integration tests dont rely on the struct for their implementation
- the exported functionality of the factory (i.e. what it needs to provide to create a scheduler configuration) is completely explicit, rather then completely coupled to a struct.
- makes some parts of the factory immutable, again to minimize possible coupling.  

This makes it easier to make a custom factory in instances where we might specifically want to import scheduler logic without actually reusing the entire scheduler codebase.