Make client handlers that call authenticated identity RPC's gated on CSAT

Summary: This diff prevents prekey handler, platform details synchronizer and user infos handler from making authorized identity calls without having CSAT.

Test Plan:
Set usingCommServicesAccessToken = false but remove if statements checking for usingCAST. Ensure that error logs for prekey handler and platform details synchronizer appear in the console. Now apply this diff and ensure that those error logs disapper.

I couldn't figure a good way to test user infos handler but I think that test plan for other components suggests that it will work too since it uses the same check.

Reviewers: inka, ashoat

Reviewed By: ashoat

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D12695