Establish olm sessions for notifs on both sides during log-in
Summary: This differential implements establishment of olm sessions for e2e notifs on both sides during log in.
Test Plan: Log in to the keyserver and examine content on olm_sessions table. New entry should appear.
Reviewers: tomek, atul, bartek, jon, ashoat
Reviewed By: ashoat
Subscribers: ashoat
Differential Revision: https://phab.comm.dev/D7654