[web] Introduce SidebarList component

Summary:
Introduce component displaying list of sidebars in Sidebars modal.

Test Plan: The component will be used in Sidebars Modal after next diff.

Reviewers: tomek, atul, ashoat

Reviewed By: tomek, ashoat

Subscribers: ashoat, adrian, abosh

Differential Revision: https://phab.comm.dev/D4609