[lib/native] lift set custom server action type into lib

Summary:
At the moment, the customServer redux field lives only in native. Since we want to use this state in web as well, we will need to lift the redux logic into lib. This diff handles lifting the set custom server action type into lib, and a subsequent diff will handle lifting the redux state into lib.

Depends on D10089

Test Plan: flow and confirmed that the custom server url on native still works as expected

Reviewers: inka, michal, rohan

Reviewed By: rohan

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D10090