[native] save the recently deleted server url to customServer redux state

Summary:
As I was organizing my Linear tasks, I realized that there was a piece of behavior with the remove keyserver user experience that I did not implement

• if a server is removed from the list, and the user is staff or in dev mode, we want this url to be saved to customServer
• if a user is staff or in dev mode, we want the input field to be pre-populated with value from customServer

This diff implements the functionality described above

Part of linear task: https://linear.app/comm/issue/ENG-4718/add-remove-keyserver-button-logic

Test Plan:
Please see the demo video below

Reviewers: inka, rohan, michal

Reviewed By: inka

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D9906