Add a config toggle to switch between full main menu and chains only menu

[tithrion]

Is your feature request related to a problem? Please describe.
On RPi5 only I have the full menu available whereas I ony have the chains menu on Zynthian v5.1 hardware.
While understanding that all (missing) entries can be reached by hardware buttons, I'd prefer being able to have the full main menu for the sake of being able to remote control (VNC) these entries also if the Zynthian is not physically in reach.

Describe the solution you'd like
Add a toggle somewhere in Admin to switch between full and chains only main menu.

Describe alternatives you've considered
I currently don't see an alternative.

Additional context
As the full menu is still available on my RPi5 whereas I have the chains only menu on my Zynthian v5.1, there must be a logic somewhere (I assume in the hardware detection/wiring logic) that already changes the menu behaviour according to available hardware.

[riban-bw]

Be aware that (almost) everything can be accessed via keyboard shortcuts or manually mapped. I use the V4 style encoder + push QWERTY mapping to control the V5 remotely and can do most things. I do miss access to audio levels, midi recorder, etc. These can be mapped to keyboard bindings.

Maybe the touchscreen option should also affect this menu selection, e.g. if "touch only" selected then show the main menu. (I can't remember if this already happens and it may be undesirable.)

I am not (yet) convinced that we want another configuration parameter so changing behaviour based on an existing config would be good.