[keyserver] Use threadIsWithBlockedUserOnlyWithoutAdminRoleCheck instead of threadFrozenDueToBlock in checkThreadsFrozen

Summary:
Context: https://linear.app/comm/issue/ENG-7249/update-checkthreadsfrozen

We do sequential fetchThreadInfos to get communityThreadInfos so we can determine whether there is an admin without "sketchy" CHANGE_ROLE permission check.

Depends on D12502

Test Plan:
flow + set some breakpoints and observed correct behavior:

Reviewers: ashoat

Reviewed By: ashoat

Differential Revision: https://phab.comm.dev/D12543