Introduce touch confirmation for reboot

[Ingo-Albrecht]

A Nitrokey 3 can be rebooted via commandline, which can be helpful. The reboot is finished instantly. This convenience feature was discussed in the trussed-dev repo. It was concluded that:

• Adding a touch confirmation to complete the reboot would ensure the user is ready to continue with the next operation.
• If touch is implemented as configurable option, it can default to on, e.g. after a device-reset.