first dest handler unittests

- Add new mock class for event reporting proxies
- Add basic setup for unittesting the CFDP destination handler

unittests/mocks/EventReportingProxyMock.cpp

@@ -0,0 +1,6 @@
+#include "EventReportingProxyMock.h"
+
+void EventReportingProxyMock::forwardEvent(Event event, uint32_t parameter1,
+                                           uint32_t parameter2) const {
+  eventQueue.emplace(event, parameter1, parameter2);
+}