Feature: #99584 - Allow to provide name for new admin users in ext:install

See forge#99584


The field realName has been added to the "Create Administrative User" modal in ext:install, so it is possible to provide the name of a new admin user.

The notice in the header of the model has been removed, since it is superfluous now.


It is now possible to provide the field realName, when a new admin user is created in ext:install.