Update unread count storage from JS and NSE

Summary: This differential uses JSI introduced in parent differential to update unread count for each keyserver from JS on native.

Test Plan:
Build iOS app and send notifications and/or update unread status on web client on both backgrounded and foregrounded app. Ensure unread count
functionality is not broken.

Reviewers: tomek, bartek, inka

Reviewed By: inka

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D11090