Creating the "First User" must be optional (or configurable)

[kobliha]

Agama will not allow clicking /Install/ before I define the first user, but there are systems that do not need the first user, e.g.., root-only systems that are managed by Salt or similar. Some servers just don't need any other users. If want it to be enforced for TW/Leap, then it needs to be configurable per product as SLES can skip creating that user.