[lib] Update genesis.id to use authoritativeKeyserverID

Summary:
issue: https://linear.app/comm/issue/ENG-6727/use-authoritativekeyserverid-in-genesis
GENESIS is the community holding DMs and thick threads for now. We want to have one GENESIS in our setups, hosted by the authoritative keyserver

Test Plan:
Tested on web and native that it is possible to create a thick thread, and no errors show up.
Checked on web that the created chat has parentThreadID: "256|1", where 256 is the value of authoritativeKeyserverID in my setup.
That checks that gnesis.id is set properly, because of code in lib/actions/thread-actions.js newTread action, which if not provided a parentThreadID uses genesis.id (I made sure that was the case)

Reviewers: michal, tomek

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D11011