[lib][web][native] Add configurable authoritativeKeyserverID

Summary:
issue: ENG-6634
We need the constant that is currently called ashoatKeyserverID to be configurable. We have two different ways of configuring things on web vs native. On native we can just import .json files. On we we cannot do that (this is complicated why, see ENG-1181 for more info), so we use a workaround. I followed D7371 for that

Test Plan:
Created authoritativeKeyserverID.json

{
  "authoritativeKeyserverID": "256"
}

in keyserver/facts and native/facts. Added a console log on both web and native and checked that value from the config is logged (it was set to something else than ashoatKeyserverID)

Reviewers: tomek, michal

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D10993