[identity] Move X3DH message types to auth proto

Summary:
Moved message types specific to GetOutboundKeys (these have been partially here already) and GetInboundKeys to the auth proto

Depends on D10050

Test Plan: Identity Service and clients still compile, I'm able to make successful RPC calls

Reviewers: varun

Reviewed By: varun

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D10051