add restart button for ESP devices

src/esp.h

@@ -60,6 +60,15 @@ namespace HaESP {
         return builder;
     }
 
+    Builder<Button>& restartButton() {
+        return Builder<Button>::instance(new Button{"Restart", "restart",
+            [](const char* msg) {
+                if (strcmp("PRESS", msg) == 0) ESP.restart();
+            }
+        })
+        .withIcon("mdi:restart");
+    }
+
     void enableSensors() {
         if (activeSensors.heapStats) tHeap.enable();
         if (activeSensors.restartInfo) tRestartInfo.enable();