Add mapping logic and serialization for writing

app/src/fan/HwmonFan.cxx

@@ -1,3 +1,4 @@
+#include <boost/json/object.hpp>
 #include <fan/HwmonFan.h>
 
 using namespace std;
@@ -9,3 +10,9 @@ HwmonFan::HwmonFan(shared_ptr<PwmControl> pwmControl,
 void HwmonFan::pwm(int percent) { mPwmControl->pwm(percent); }
 
 int HwmonFan::rpm() { return mRpmSensor->value(); }
+
+json HwmonFan::toJson() const {
+  json obj;
+  obj["HwmonFan"] = {mPwmControl->toJson(), mRpmSensor->toJson()};
+  return obj;
+}