[web] Move up ComponentDid[Mount/Update] functionality to ConnectedThreadSettingsModal useEffect

Summary:
Move the componentDidMount and componentDidUpdate lifecycle handlers to a useEffect in the outer "Connected" component.

As part of the work to refactor ThreadSettingsModal... specifically to turn it into a functional component (any day now...)

Depends on D3796

Test Plan: Haven't tested yet, will need to set up multiple users/clients to test

Reviewers: def-au1t, palys-swm, ashoat

Reviewed By: palys-swm, ashoat

Subscribers: ashoat, Adrian, karol-bisztyga, benschac, yayabosh

Differential Revision: https://phabricator.ashoat.com/D3797