Adding full DI navigation example for testing purposes.

- adding internal private field into FormBase class
- adding Extension methods into DependencyInjection namespace for use
- adding 2 NavigateTo extension methods for DI using ServiceProvider
- adding example project
- adding to readme as example

TelegramBotBase/Factories/ServiceProviderStartFormFactory.cs

@@ -1,5 +1,6 @@
 using System;
 using Microsoft.Extensions.DependencyInjection;
+using TelegramBotBase.DependencyInjection;
 using TelegramBotBase.Form;
 using TelegramBotBase.Interfaces;
 
@@ -16,14 +17,19 @@ public class ServiceProviderStartFormFactory : IStartFormFactory
         {
             throw new ArgumentException($"{nameof(startFormClass)} argument must be a {nameof(FormBase)} type");
         }
-
+        
         _startFormClass = startFormClass;
         _serviceProvider = serviceProvider;
     }
 
     public FormBase CreateForm()
     {
-        return (FormBase)ActivatorUtilities.CreateInstance(_serviceProvider, _startFormClass);
+        var fb = (FormBase)ActivatorUtilities.CreateInstance(_serviceProvider, _startFormClass);
+
+        //Sets an internal field for future ServiceProvider navigation
+        fb.SetServiceProvider(_serviceProvider);
+
+        return fb;
     }
 }