Add an external watchdog module

src/helpers/ExWatchdogManager.h

@@ -0,0 +1,11 @@
+#pragma once
+
+class ExWatchdogManager {
+public:
+  unsigned long next_feed_watchdog;
+  ExWatchdogManager() { next_feed_watchdog = 0; }
+  virtual bool begin() { return false; }
+  virtual void loop() { }
+  virtual unsigned long getIntervalMs() const { return 0; }
+  virtual void feed() { }
+};