[native] introduce Add keyserver screen UI

Summary:
This diff introduces and implements the UI for the add keyserver screen. The logic for the onPressSave callback will be implemented in subsequent diffs

Figma designs:

Linear task: https://linear.app/comm/issue/ENG-5409/implement-ui-for-the-add-keyserver-input-screen

Depends on D9587

Test Plan:
Please see the demo video below

Reviewers: inka, rohan, michal

Reviewed By: michal

Subscribers: ashoat, tomek, wyilio

Differential Revision: https://phab.comm.dev/D9590