Refactor: split optimizer-schema.json into multiple files

[bpkroth]

          Future work, but we should probably split this schema up into smaller files like we do for the other schemas.

Originally posted by @bpkroth in #855 (comment)

[Sarishc]

Hi, I would like to work on this issue. Could you please assign it to me and explain how the file should be refactored?

[bpkroth]

Sure, have a look at this set of schemas for Service configs:
https://github.com/microsoft/MLOS/tree/main/mlos_bench/mlos_bench/config/schemas/services

At a high level services-schema.json specifies the rough schema that all Services must follow by saying it should be one of several child Services, each of which's own config is specified in its own file.

We want to do the same thing here.