Hotkeys for grid should be configurable independently for schematic/board

Description

Changing the grid in schematic often happens by accident. The n key is pretty close to the heavily used m key. See https://chaos.social/@azonenberg@ioc.exchange/110370620557992208

Ideally those two uses for the grid settings can be configured independently. A alternate workflow to solve this usability issue would be an option to lock the grid.

Steps to reproduce

1. Open Preferences->Hotkey
2. Search for grid
3. The default hotkey n and SHIFT+n are the same for schematic and layout

KiCad Version

Application: KiCad Schematic Editor x86_64 on x86_64

Version: 7.0.2, release build

Libraries:
	wxWidgets 3.2.2
	FreeType 2.12.1
	HarfBuzz 5.2.0
	FontConfig 2.14.1
	libcurl/7.86.0-DEV OpenSSL/3.0.8 zlib/1.2.13 nghttp2/1.52.0

Platform: Linux 6.1.0-7-amd64 x86_64, 64 bit, Little endian, wxGTK, i3, x11

Build Info:
	Date: Apr 24 2023 05:57:08
	wxWidgets: 3.2.2 (wchar_t,wx containers) GTK+ 3.24
	Boost: 1.82.0
	OCC: 7.7.0
	Curl: 7.86.0-DEV
	ngspice: 40
	Compiler: GCC 12.2.0 with C++ ABI 1017

Build settings:
	KICAD_SPICE=ON