Allow to use different image driver in Create User command

[luchaos]

Currently locked-in to imagick. Should allow to use Identicon\Generator\GdGenerator as well. This would be in line with media-package where it's allowed to switch between gd and imagick drivers.

admin-package/src/Command/User/CreateUserCommand.php

Line 85 in fc509b5

$identicon = new Identicon(new ImageMagickGenerator());