[lib/native] extend keyserverAdminUsername to be keyserverAdminUserInfo

Summary:
The remove keyserver action needs the keyserver admin user id. I realized as I was implementing the solution to remove a keyserver from the keyserver store that I am only had the username available to me. This diff extends the keyserverAdminUsername to be keyserverAdminUserInfo which also holds the keyserver admin user id

Depends on D9806

Test Plan: flow and confirmed that I now have the userID in the keyserverAdminUserInfo

Reviewers: inka, rohan, michal

Reviewed By: inka

Subscribers: ashoat, tomek, wyilio

Differential Revision: https://phab.comm.dev/D9826