[lib] Fix unable to register new user

Summary:
issue: https://linear.app/comm/issue/ENG-6309/unable-to-connect-to-ashoats-keyserver-during-new-registration-flow
This is a super quick fix because this issue is blocking other devs.
The problem was that it was not possible to register a new user, even with Ashoat's keyserver picked

The reason for this happening is that when we are connecting to a new keyserver we don't know its id. So to be able to call it with our actions we create paramOverride, which includes keyserverInfos. In those keyserverInfos the key is the urlPrefix, not admins id. This keyserver is later on added to the store by a setNewSessionActionType.
So what happens in the new registration flow is that when a user selects Ashoat's keyserver, a new entry is added to the keyserverStore.keyserverInfos, with its key being defaultURLPrefix. This entry is broken - hence the missing status, which will be fixed by ENG-6097. But we should either way be using the entry for Ashoat's keyserver that is already in our store.

Test Plan: Tested that it is possible to register a user with the new registration flow, provided Ashoat's keyserver is picked

Reviewers: ginsu, ashoat

Reviewed By: ginsu, ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D10479