Allow disable of POWER_TIMEOUT (#21771)

Co-authored-by: Scott Lahteine <github@thinkyhead.com>

Marlin/src/feature/power.cpp

   return false;
 }
 
+#ifndef POWER_TIMEOUT
+  #define POWER_TIMEOUT 0
+#endif
+
 void Power::check() {
   static millis_t nextPowerCheck = 0;
   millis_t ms = millis();
     nextPowerCheck = ms + 2500UL;
     if (is_power_needed())
       power_on();
-    else if (!lastPowerOn || ELAPSED(ms, lastPowerOn + SEC_TO_MS(POWER_TIMEOUT)))
+    else if (!lastPowerOn || (POWER_TIMEOUT > 0 && ELAPSED(ms, lastPowerOn + SEC_TO_MS(POWER_TIMEOUT))))
       power_off();
   }
 }