Add initial implementation of API, database, and user management components.

MikrocopApi/Exceptions/AppException.cs

@@ -0,0 +1,11 @@
+namespace MikrocopApi.Exceptions;
+
+public abstract class AppException : Exception
+{
+    protected AppException(string message) : base(message)
+    {
+    }
+
+    public abstract int StatusCode { get; }
+    public abstract string Title { get; }
+}