Save persistent triggers to storage

Create json storage file for persistent triggers.
Handle persistent dbus property.
Save/remove persistent triggers on add/delete.
Cover code with UTs.

Tested:
   - Passed unit tests
   - Tested on QEMU
     * adding new valid and invalid trigger from cli
     * verifying if valid trigger is properly stored
     * deleting existed trigger from storage

Change-Id: I243326e84833a8cb22075fbf565573b62b205b4a
Signed-off-by: Cezary Zwolak <cezary.zwolak@intel.com>
Signed-off-by: Lukasz Kazmierczak <lukasz.kazmierczak@intel.com>
diff --git a/src/telemetry.hpp b/src/telemetry.hpp
index fb7f2a3..be2d81c 100644
--- a/src/telemetry.hpp
+++ b/src/telemetry.hpp
@@ -25,6 +25,9 @@
             objServer),
         triggerManager(std::make_unique<TriggerFactory>(
                            bus, objServer, sensorCache, reportManager),
+                       std::make_unique<PersistentJsonStorage>(
+                           interfaces::JsonStorage::DirectoryPath(
+                               "/var/lib/telemetry/Triggers")),
                        objServer)
     {}