Update on "[1/N] Add BackendOptions class"

Introduce backend option as discussed in #10216

Step 1: Introducd Backend Option class

In later stage, it will be plugged in with the rest of the stack. BackendOptions is pretty much a list of BackendOption, and backend option is a key value pair. The key is a string, and the value can be 3 different types, including bool, string and int.


Differential Revision: [D75993712](https://our.internmc.facebook.com/intern/diff/D75993712/)

Differential Revision: [D75993712](https://our.internmc.facebook.com/intern/diff/D75993712)

[ghstack-poisoned]

Author: cccclai