[identity] Allow v1 login for authoritative keyserver

Summary: Address ENG-10012.

Test Plan: Mocked AUTHORITATIVE_KEYSERVER_OWNER_USER_ID with my user ID and verified that v1 login works for my keyserver despite having signed device list

Reviewers: kamil

Reviewed By: kamil

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D14172