Add boot from EMMC to dietpi-config

[keeno1982]

That would be very convenient if a tool integration in dietpi-config. Flash to EMMC or to USB and SD, we just need one key choose . I really hope you consider this feature, thanks : )

Picture from armbian-config

[MichaIng]

For partitioning/filesystem formatting we can follow the method of our image build script: https://github.com/MichaIng/DietPi/blob/dev/.build/images/dietpi-build

For bootloader/cmdline/fstab adjustments, dietpi-backup does this to assure that restoring an old backup onto a new system (changed UUID) does not break book: https://github.com/MichaIng/DietPi/blob/e9201a1/dietpi/dietpi-backup#L237