Update APITemplateCreator.cs to pickup correct displayName and keeping backward compatibility when displayName is not provided in config (#421)

Author: vibindal

src/APIM_ARMTemplate/apimtemplate/Creator/TemplateCreators/APITemplateCreator.cs

@@ -136,7 +136,7 @@ public async Task<APITemplateResource> CreateAPITemplateResourceAsync(APIConfig
                 apiTemplateResource.properties.subscriptionKeyParameterNames = api.subscriptionKeyParameterNames;
                 apiTemplateResource.properties.path = api.suffix;
                 apiTemplateResource.properties.isCurrent = api.isCurrent;
-                apiTemplateResource.properties.displayName = api.name;
+                apiTemplateResource.properties.displayName = string.IsNullOrEmpty(api.displayName) ? api.name : api.displayName;
                 apiTemplateResource.properties.protocols = this.CreateProtocols(api);
                 // set the version set id
                 if (api.apiVersionSetId != null)