[lib/web] introduce useThreadSettingsNotifications

Summary: This diff introduces a new hook called useThreadSettingsNotifications which factors out all the shared thread notification settings logic that will be used in both web and native

Test Plan: Confirmed that there were no regresssions with the notifications modal on web

Reviewers: ashoat, inka

Reviewed By: ashoat, inka

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D12646