[web] Introduce AddMembersItem component

Summary:
Introduce component rendering single user on the list in AddMembersModal. Because I shared some common logic with native, user information are passed in UserListItem type.

GIF presenting the items:

Test Plan: Component can be tested after introducing AddMembersModal

Reviewers: palys-swm, atul, benschac

Reviewed By: palys-swm

Subscribers: ashoat, palys-swm, Adrian, atul, karol-bisztyga, benschac, yayabosh

Differential Revision: https://phabricator.ashoat.com/D3739