feat: Add ADC sensor device tree bindings and configuration

Introduces device tree bindings for custom ADC voltage and current sensors,
allowing for flexible configuration of sensor inputs and associated GPIOs.
This enables proper hardware abstraction for ADC measurements.

The example overlay file
has been removed as its content is now integrated or superseded by the new
binding definitions.

software/.vscode/settings.json

@@ -9,4 +9,7 @@
 		"app_version.h": "c"
 	},
 	"C_Cpp.clang_format_style": "file",
+	"nrf-connect.applications": [
+		"${workspaceFolder}/apps/slave_node"
+	],
 }