feat: CurrencyExchangeRequest with validator and validator's tests outline

src/main/java/eu/ztsh/wymiana/validation/ValidExchangeRequest.java

@@ -0,0 +1,24 @@
+package eu.ztsh.wymiana.validation;
+
+import jakarta.validation.Constraint;
+import jakarta.validation.Payload;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.Retention;
+import java.lang.annotation.Target;
+
+import static java.lang.annotation.ElementType.TYPE_USE;
+import static java.lang.annotation.RetentionPolicy.RUNTIME;
+
+
+@Retention(RUNTIME)
+@Target({ TYPE_USE })
+@Documented
+@Constraint(validatedBy = {ValidExchangeRequestValidator.class })
+public @interface ValidExchangeRequest {
+
+    String message() default "Exchange request is not valid";
+    Class<?>[] groups() default { };
+    Class<? extends Payload>[] payload() default { };
+
+}