createuser: Update docs to reflect defaults

createuser: Update docs to reflect defaults

Commit c7eab0e97 changed the default password_encryption setting to
'scram-sha-256', so update the example for creating a user with an
assigned password.

In addition, commit 08951a7c9 added new options that in turn pass
default tokens NOBYPASSRLS and NOREPLICATION to the CREATE ROLE
command, so fix this omission as well for v16 and later.

Reported-by: Heikki Linnakangas <hlinnaka@iki.fi>
Discussion: https://postgr.es/m/cff1ea60-c67d-4320-9e33-094637c2c4fb%40iki.fi
Backpatch-through: 14