997818: Need to Provide Sample Code on ComboBox custom-value section

### Task Link 
[997818](https://dev.azure.com/EssentialStudio/Ej2-Web/_workitems/edit/997818) : Need to Provide Sample Code on ComboBox customer value section

### Ticket Link 
https://support.syncfusion.com/agent/tickets/793286  

### What corrected?
Updated Sample Code on ComboBox custom-value section

### Screenshot or Gif
Nil

Author: sureshsf3950

blazor/combobox/custom-value.md

@@ -13,4 +13,10 @@ Enable users to enter values that are not present in the data by using the [Allo
 
 To persist the new entry to the underlying data source, handle application logic (for example, in value change handling) to add the custom value to the collection. Users can also commit a custom value with the keyboard (such as pressing Enter) when appropriate.
 
+{% highlight cshtml %}
+
+{% include_relative code-snippet/custom-value/custom-value.razor %}
+
+{% endhighlight %}
+
 {% previewsample "https://blazorplayground.syncfusion.com/embed/LDBACVLQKFyiyoKz?appbar=false&editor=false&result=true&errorlist=false&theme=bootstrap5" backgroundimage "[Blazor ComboBox with custom value](./images/blazor-combobox-custom-value.png)" %}