Define MaxConcurrentSessions property for Manager.SerialConsole and GraphicalConsole

This is required feature

Tested:
1. Verified by Readfish Service Validator.
2. https://IP_ADDR/redfish/v1/Managers/bmc
"GraphicalConsole": {
  "ConnectTypesSupported": ["KVMIP"],
  "MaxConcurrentSessions": 1,
  "ServiceEnabled": true
}
"SerialConsole": {
  "ConnectTypesSupported": ["IPMI", "SSH"],
  "MaxConcurrentSessions": 15,
  "ServiceEnabled": true
}

Change-Id: I01700085f4d9d7f3a4aa80fa4240ed201e948159
Signed-off-by: Kuiying Wang <kuiying.wang@intel.com>
diff --git a/redfish-core/lib/managers.hpp b/redfish-core/lib/managers.hpp
index 9db714b..12ed177 100644
--- a/redfish-core/lib/managers.hpp
+++ b/redfish-core/lib/managers.hpp
@@ -1583,12 +1583,15 @@
 
         res.jsonValue["DateTime"] = crow::utility::dateTimeNow();
 
-        // Fill in GraphicalConsole and SerialConsole info
+        // Fill in SerialConsole info
         res.jsonValue["SerialConsole"]["ServiceEnabled"] = true;
+        res.jsonValue["SerialConsole"]["MaxConcurrentSessions"] = 15;
         res.jsonValue["SerialConsole"]["ConnectTypesSupported"] = {"IPMI",
                                                                    "SSH"};
 #ifdef BMCWEB_ENABLE_KVM
+        // Fill in GraphicalConsole info
         res.jsonValue["GraphicalConsole"]["ServiceEnabled"] = true;
+        res.jsonValue["GraphicalConsole"]["MaxConcurrentSessions"] = 1;
         res.jsonValue["GraphicalConsole"]["ConnectTypesSupported"] = {"KVMIP"};
 #endif // BMCWEB_ENABLE_KVM