🚸 Up to 10 Preheat Constants (#24636)

Marlin/Configuration.h

 // @section temperature
 
 //
-// Preheat Constants - Up to 6 are supported without changes
+// Preheat Constants - Up to 10 are supported without changes
 //
 #define PREHEAT_1_LABEL       "PLA"
 #define PREHEAT_1_TEMP_HOTEND 180

Marlin/src/inc/Conditionals_post.h

 #endif
 
 #if HAS_TEMPERATURE && ANY(HAS_MARLINUI_MENU, HAS_DWIN_E3V2, HAS_DGUS_LCD_CLASSIC)
-  #ifdef PREHEAT_6_LABEL
+  #ifdef PREHEAT_10_LABEL
+    #define PREHEAT_COUNT 10
+  #elif defined(PREHEAT_9_LABEL)
+    #define PREHEAT_COUNT 9
+  #elif defined(PREHEAT_8_LABEL)
+    #define PREHEAT_COUNT 8
+  #elif defined(PREHEAT_7_LABEL)
+    #define PREHEAT_COUNT 7
+  #elif defined(PREHEAT_6_LABEL)
     #define PREHEAT_COUNT 6
   #elif defined(PREHEAT_5_LABEL)
     #define PREHEAT_COUNT 5