[web] Merge store and server search results

Summary:
Merge the results from both sources and store them in a memo.

Depends on D4268

Test Plan: Render the component and check if merged result contains only the users matched by the search text.

Reviewers: def-au1t, atul, benschac

Reviewed By: atul

Subscribers: ashoat, Adrian, yayabosh

Differential Revision: https://phab.comm.dev/D4269