[scripts] Improve prompt

Summary:
issue: ENG-7310
The admin of the new keyserver has to be a user that was not an admin befroe. They don't have to exist on the identity service though, registration will be attempted

Test Plan: Ran nix develop, typed y and checked that the propmt is printed correctly

Reviewers: will, kamil

Reviewed By: will

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D11530