Utilise subscription from ThickMemberInfo when building a notif

Summary: This differential extracts a common logic that uses thread subscription, user role and mentioning to decide whether to send a notif. Moreover this logic is used in the client-send code.

Test Plan:

1. Test that chat muting and user mentioning (also for ENS users) works on the keyserver from the notif perspective.
2. To test the client, apply patch from D12477 and then:
   1. Without any changes there should be no notif payloads generated.
   2. Play around with hardcoding different configurations of thread subscriptions and examine content of generated notifs.

Reviewers: kamil, tomek

Reviewed By: kamil

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D12539