## What
Fix typing on ShippingOptionService.list selector parameter
## Why
A backend server interfacing with the `ShippingOptionService.list()` method will throw TS error when attempting to pass selector values that should be valid.
## Steps to reproduce
* In a IDE that can display TS errors
* Create an instance of the ShippingOptionService
* Call the `list()` method on the instance with the following selector parameter: `{ region_id: "foobar" }`
* Expect: No TS error
* Actual: `TS2345: Argument of type '{ region_id: string; }' is not assignable to parameter of type 'Selector<ShippingMethod>'.`
## How
* Change the `selector` type to `Selector<ShippingOption>`
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