feat(matter_example): use const char * instead of #define

Author: SuGlider

Diff for: libraries/Matter/examples/MatterDimmableLight/MatterDimmableLight.ino

@@ -22,9 +22,9 @@
 MatterDimmableLight DimmableLight;
 
 // it will keep last OnOff & Brightness state stored, using Preferences
-Preferences lastStatePref;
-#define ON_OFF_PREF_KEY     "lastOnOffState"
-#define BRIGHTNESS_PREF_KEY "lastBrightness"
+Preferences matterPref;
+const char *onOffPrefKey = "OnOffState"
+const char *brightnessPrefKey = "BrightnessState"
 
 // set your board RGB LED pin here
 #ifdef RGB_BUILTIN
@@ -53,8 +53,8 @@ bool setLightState(bool state, uint8_t brightness) {
     digitalWrite(ledPin, LOW);
   }
   // store last Brightness and OnOff state for when the Light is restarted / power goes off
-  lastStatePref.putUChar(BRIGHTNESS_PREF_KEY, brightness);
-  lastStatePref.putBool(ON_OFF_PREF_KEY, state);
+  matterPref.putUChar(brightnessPrefKey, brightness);
+  matterPref.putBool(onOffPrefKey, state);
   // This callback must return the success state to Matter core
   return true;
 }
@@ -88,11 +88,11 @@ void setup() {
   delay(500);
 
   // Initialize Matter EndPoint
-  lastStatePref.begin("matterLight", false);
+  matterPref.begin("MatterPrefs", false);
   // default OnOff state is ON if not stored before
-  bool lastOnOffState = lastStatePref.getBool(ON_OFF_PREF_KEY, true);
+  bool lastOnOffState = matterPref.getBool(onOffPrefKey, true);
   // default brightness ~= 6% (15/255)
-  uint8_t lastBrightness = lastStatePref.getUChar(BRIGHTNESS_PREF_KEY, 15);
+  uint8_t lastBrightness = matterPref.getUChar(brightnessPrefKey, 15);
   DimmableLight.begin(lastOnOffState, lastBrightness);
   // set the callback function to handle the Light state change
   DimmableLight.onChange(setLightState);