[keyserver] return threadInfo in fetchAllCommunityInfosWithNames

Summary:
Depends on D13853

we return threadInfos here so that we can populate the community directory on clients using the ThreadList component

Test Plan: tested in next diff by calling fetchAllCommunityInfosWithNames and getting a working modal with the ThreadList correctly populated

Reviewers: ashoat

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D13854