[keyserver] Add a function which checks if a keyserver is authoritative

Summary:
On prod, only Ashoat's keyserver is authoritative.
On our local environments, we usually run the authoritative keyserver using yarn dev. Additional keyserver are run using docker, which calls npm prod beneath.

https://linear.app/comm/issue/ENG-7842/create-an-env-variable-that-tells-if-we-should-create-a-genesis

Test Plan: Run a local keyserver and check if the function returns true. Run a keyserver in docker and check if the function returns false.

Reviewers: inka, ginsu

Reviewed By: inka

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D12226