[web] Memoize NotificationsOption onSelect prop w/ useCallback hook

Summary: The NotificationsOption onSelect callback prop was being defined inline instead of being memoized with React.useCallback. This diff just fixes that.

Test Plan: Clicked through the NotificationsModal and things worked as expected.

Reviewers: def-au1t, palys-swm, benschac, yayabosh

Reviewed By: palys-swm, yayabosh

Subscribers: ashoat, Adrian, yayabosh

Differential Revision: https://phabricator.ashoat.com/D4042