Created metric class

Metric collects updates from sensor. Report displays metric readings
depending on reportingType.

Tested:
  - Added new units tests for Metric class
  - All other unit tests are passing

Change-Id: I19f4831fab163a4f9540cef7bb23e903ae90fddf
Signed-off-by: Krzysztof Grobelny <krzysztof.grobelny@intel.com>
diff --git a/src/telemetry.hpp b/src/telemetry.hpp
index 4a6a6b0..4cc138e 100644
--- a/src/telemetry.hpp
+++ b/src/telemetry.hpp
@@ -3,6 +3,7 @@
 #include "persistent_json_storage.hpp"
 #include "report_factory.hpp"
 #include "report_manager.hpp"
+#include "sensor_cache.hpp"
 
 #include <sdbusplus/asio/connection.hpp>
 #include <sdbusplus/asio/object_server.hpp>