[lib] refactor set new session in keyserver-reducer to ops

Summary:
Convert logic to ops approach.

Depends on D10759

Test Plan:

1. Refresh website on web (it cause sessionChange with defined cookie).
2. Make sure state changes the same way as before refactor.

Reviewers: inka, ashoat

Reviewed By: inka, ashoat

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D10760