Refactored endpoints to be more functional and more expressive

PostFundManagement.Domain/Errors/ValidationError.cs

@@ -0,0 +1,14 @@
+namespace PostFundManagement.Domain.Errors;
+
+public sealed class ValidationError : Error
+{
+    public static ValidationError New { get; } = new();
+
+    public ValidationError() : base(string.Empty) { }
+
+    public ValidationError(string message) : base(message) { }
+
+    public static ValidationError Create() => new();
+
+    public static ValidationError Create(string message) => new(message);
+}