[lib] Hide initialThreadState.memberIDs from GENESIS
Summary:
We hide the members list of GENESIS. For similar reasons, we should hide the list of initial members.
This addresses ENG-9430; more context there.
Test Plan: I added an || true, and then logged out and back in on web and confirmed that all thread creation robotext were missing "and added A and B" at the end
Reviewers: varun, will
Reviewed By: will
Subscribers: tomek
Differential Revision: https://phab.comm.dev/D13528