[lib] Refactor lastCommunicatedPlatformDetails to be PlatformDetails

Summary:
issue: https://linear.app/comm/issue/ENG-4462/refactor-lastcommunicatedplatformdetails-field
I want to put lastCommunicatedPlatformDetails inside of keyserverStore. It will be much easier if lastCommunicatedPlatformDetails is first refatored to
be a single field of PlatformDetails type, mostly becuse the reducer will be possible to reuse in reduceKeyserverStore

Test Plan: ran yarn flow-all.

Reviewers: michal, kamil

Reviewed By: michal

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D9060