Event: Change MemberId type to string

The type of the MemberId according to the schema
https://redfish.dmtf.org/schemas/v1/Event.v1_4_0.json is string
and not int.  This prevents the request from being deserialized
by clients written in typed languages.

Change-Id: Ic1a00044fdb71e20cb96d4256e935f59bf79da8f
Signed-off-by: Igor Kanyuka <ifelmail@gmail.com>
diff --git a/redfish-core/include/event_service_manager.hpp b/redfish-core/include/event_service_manager.hpp
index f6d36de..bb722f3 100644
--- a/redfish-core/include/event_service_manager.hpp
+++ b/redfish-core/include/event_service_manager.hpp
@@ -314,7 +314,7 @@
         logEntryJson["Message"] = "Generated test event";
         logEntryJson["MessageId"] = "OpenBMC.0.2.TestEventLog";
         // MemberId is 0 : since we are sending one event record.
-        logEntryJson["MemberId"] = 0;
+        logEntryJson["MemberId"] = "0";
         logEntryJson["MessageArgs"] = nlohmann::json::array();
         logEntryJson["EventTimestamp"] =
             redfish::time_utils::getDateTimeOffsetNow().first;
@@ -978,7 +978,7 @@
         eventMessage["OriginOfCondition"] = origin;
 
         // MemberId is 0 : since we are sending one event record.
-        eventMessage["MemberId"] = 0;
+        eventMessage["MemberId"] = "0";
 
         messages.push_back(Event(std::to_string(eventId), eventMessage));