[lib] Make activity-handler keyserver-specific

Summary:
Add a prop that identifies a keyserver.
Make sure that we queue only the updates to a keyserver that owns a thread.

https://linear.app/comm/issue/ENG-5777/update-activityhandler

Depends on D11089

Test Plan:
Focus a thread and check if the action is dispatched.
Using React debugger, modified ActionHandler's activeThread prop to a thread that has a different prefix - that resulted in only one, focus: false update being generated. Changed it back to the correct prefix - again, only one update was generated (this time focus: true).

Reviewers: inka, kamil, michal, atul

Reviewed By: inka

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D11092