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

Summary:
issue: https://linear.app/comm/issue/ENG-4460/refactor-connection-field
First step is to add connection field to keyserverStore

Test Plan: ran yarn flow-all

Reviewers: michal, kamil

Reviewed By: michal

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8924