Add sysroot prepare support

[wintron04]

Major reworks:

Biggest change is probably that now for building berrymill needs to be explicitly called with the build option

e.g. berrymill -i /path/to/appliance.xml build --target-dir /path/to/targetdir

• Improved Parameter parsing
• Added Subparser (build, prepare)
• Support for kiwi-ng system prepare
• Added no-accel for boxbuilding
• Added allow-existing-root for prepare
• minimize reduntant code with better inheritance
• Introduced class KiwiParent for kiwi Repo Handling
• Split classes in differnt files
• Unit Test adjustemnt to follow to new code layout
• config enhancement: Useful config

Introduction of berrymill prepare

Usage:

berrymill -i /path/to/appliance.xml [global options] {prepare,build} [specific options]

run berrymill -h for more details.

[isbm]

@wintron04 I think you need to rebase it on main, because paths were changed.

[isbm]

What is happening here?? You supposed to rebase your stuff, not cherrypick 90+ commits 🤣