[keyserver][lib][native] Add connection to keyserverStore

Summary: issue: https://linear.app/comm/issue/ENG-4460/refactor-connection-field

Test Plan: ran yarn flow-all. Checked that the user is not getting logged out after app restart (context: https://linear.app/comm/issue/ENG-4809/logout-triggered-on-app-restart)

Reviewers: michal, kamil

Reviewed By: michal

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D9021