Update extractKeyserverIDFromID so that it returns null for DMs

Summary:
This requires changes in a lot of places because we were assuming that a thread ID is present.

https://linear.app/comm/issue/ENG-8427/make-sure-we-dont-run-keyserver-client-state-check-on-e2ee-dms

Test Plan: Mostly Flow. Tested some simple scenarios, e.g. sending a message.

Reviewers: inka, bartek

Reviewed By: inka, bartek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D12650