Create a buck genrule for schema_generated.h

Summary:
Create a buck genrule for schema_generated.h
- Genrule example: https://www.internalfb.com/code/fbsource/[6e2ed7840cb2]/fbcode/executorch/schema/targets.bzl?lines=20-41

This is needed to add dependency of qualcomm/schema_generated.h into the ET-QNN for Meta Wearable app

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Reviewed By: kirklandsign

Differential Revision: D60456032

fbshipit-source-id: fbf30b3b3468aca5f287f0ab159701e553dc5db7