Update base for Update on "[4/N] Add backend options map"

This is to manage the backend <-> BackendOptions map. Users will create the bakcend options map, and ET runtime will read the backend name, and dispatch the list of backend options to each backend.

Differential Revision: [D76149466](https://our.internmc.facebook.com/intern/diff/D76149466/)

[ghstack-poisoned]

Author: cccclai