C# Bindings - Prompt formatting (#712)

* Added support for custom prompt formatting

* more docs added

* bump version

gpt4all-bindings/csharp/Gpt4All/Model/DefaultPromptFormatter.cs

@@ -0,0 +1,16 @@
+namespace Gpt4All;
+
+public class DefaultPromptFormatter : IPromptFormatter
+{
+    public string FormatPrompt(string prompt)
+    {
+        return $"""
+        ### Instruction: 
+        The prompt below is a question to answer, a task to complete, or a conversation
+        to respond to; decide which and write an appropriate response.
+        ### Prompt:
+        {prompt}
+        ### Response:
+        """;
+    }
+}