Move the [mcu] serial line creation into printer.cfg and not in ratos.cfg from RatOS-Configurator

[smwoodward-beep]

Is your feature request related to a problem? Please describe

If a user wants to change their communication method for MCU's, this change would be over written or blocked (if ratos.cfg is changed to read only).

Describe the solution you'd like

Have
[mcu]
serial:

moved to printer.cfg to allow deleting the serial line if the user chooses to do this modification. This will allow the user to keep their communication method and allow furture updates from RatOS to edit ratos.cfg

Describe alternatives you've considered

Creating a copy of ratos.cfg and changing the include in printer.cfg works to allows changes to be made, but if there is a mistake, for example pin assignments for the user selected mcu, are pushed in an update, if the user creates their own ratos.cfg and changes the include, the user will not automatically get the updated changes.

Additional information

No response