Add singleton's EntitySet URL to the odata.id URL

This is for the C# generated templates.
Currently in the templates, we generate @odata.id based off an EntitySet name, which is an absolute URL. In the case of a singleton, we want to navigate to that singleton's relevant EntitySet

Author: Caitlin Bales (MSFT)

Templates/CSharp/Base/CollectionRequest.Base.template.tt

@@ -137,6 +137,11 @@ public string GetPostAsyncMethodForReferencesRequest(OdcmProperty odcmProperty)
     var serviceNavigationProperty = odcmProperty.GetServiceCollectionNavigationPropertyForPropertyType();
 	if (serviceNavigationProperty == null)
 		return string.Empty;
+	
+	//Append the singleton's navigation type to the @odata.id if relevant
+	var implicitNavigationProperty = string.Empty;
+	if (serviceNavigationProperty.GetType() == typeof(OdcmSingleton)) 
+		implicitNavigationProperty = "/" + odcmProperty.Name;
 
     var stringBuilder = new StringBuilder();
 
@@ -178,7 +183,7 @@ public string GetPostAsyncMethodForReferencesRequest(OdcmProperty odcmProperty)
     stringBuilder.Append("            }");
     stringBuilder.Append(Environment.NewLine);
     stringBuilder.Append(Environment.NewLine);
-    stringBuilder.AppendFormat("            var requestBody = new ReferenceRequestBody {{ ODataId = string.Format(\"{{0}}/{0}/{{1}}\", this.Client.BaseUrl, {1}.Id) }};", serviceNavigationProperty.Name, sanitizedPropertyName);
+    stringBuilder.AppendFormat("            var requestBody = new ReferenceRequestBody {{ ODataId = string.Format(\"{{0}}/{0}{1}/{{1}}\", this.Client.BaseUrl, {2}.Id) }};", serviceNavigationProperty.Name, implicitNavigationProperty, sanitizedPropertyName);
     stringBuilder.Append(Environment.NewLine);
     stringBuilder.AppendFormat("            return this.SendAsync(requestBody, cancellationToken);");
     stringBuilder.Append(Environment.NewLine);