[native] implement onPressSave keyserver button callback

Summary:
This diff implements onPressSave keyserver button. This callback will create the payload necessary for this action and dispatch the add keyserver redux action we just introduced with the payload we just created. For now we will just use the current user id as the keyserver admin user id until ENG-5282 is done and returns a userID

In a subsequent diff we will implement validation that will be used before we introduce the keyserver

Linear task: https://linear.app/comm/issue/ENG-5338/dispatch-addkeyserver-redux-action

Depends on D9664

Test Plan:
Please see the demo video below

Reviewers: inka, rohan, michal

Reviewed By: inka

Subscribers: ashoat, tomek, wyilio

Differential Revision: https://phab.comm.dev/D9665