added validators in project

BookHive/Validators/Loans/PatchLoanDtoValidator.cs

@@ -0,0 +1,15 @@
+using BookHive.Endpoints.Loans;
+using FastEndpoints;
+using FluentValidation;
+
+namespace BookHive.Validators.Loans;
+
+public class PatchLoanDtoValidator : Validator<PatchReturnLoanRequest>
+{
+    public PatchLoanDtoValidator()
+    {
+        RuleFor(x => x.Id)
+            .GreaterThan(0)
+            .WithMessage("Id is invalid");
+    }
+}