Script should do pre-flight check for access to autounattend.xml

[FelixJongleur42]

People tend to only download the ps1 file, not the autounattend.xml file.
The script should do a pre-flight check for access to autounattend.xml before it even starts processing the image, so this does not occur mid-flight:

Copy-Item : Der Pfad "C:\Users\flori\Downloads\autounattend.xml" kann nicht gefunden werden, da er nicht vorhanden ist.
In C:\Users\flori\Downloads\tiny11maker.ps1:237 Zeichen:1
+ Copy-Item -Path "$PSScriptRoot\autounattend.xml" -Destination "$Scrat ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : ObjectNotFound: (C:\Users\flori\...utounattend.xml:String) [Copy-Item], ItemNotFoundException

Even better, it should create autounattend.xml on-the-fly.