[native] update userAlreadyExists in ConnectEthereum component

Summary:
We need to also check if the wallet address is reserved

Depends on D11320

Test Plan: Tried registering a wallet that was in the reserved users table. i was navigated to the existing ethereum account component.

Reviewers: ashoat

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D11321