feat: finish porting azure function to .NET 5

Habittodo.FunctionApp/Program.cs

@@ -0,0 +1,17 @@
+using Microsoft.Extensions.Configuration;
+using System.IO;
+using Microsoft.Extensions.Hosting;
+
+namespace Habittodo.FunctionApp
+{
+    public class Program
+    {
+        public static void Main()
+        {
+            var host = new HostBuilder()
+                .ConfigureFunctionsWorkerDefaults()
+                .Build();
+            host.Run();
+        }
+    }
+}