feat(EntityNotFoundException): creada excepción personalizada para entidades no encontradas

src/main/java/com/example/apprecetas/exceptions/EntityNotFoundException.java

+package com.example.apprecetas.exceptions;
+
+import org.springframework.http.HttpStatus;
+import org.springframework.web.bind.annotation.ResponseStatus;
+
+@ResponseStatus(HttpStatus.NOT_FOUND)
+public class EntityNotFoundException extends RuntimeException {
+    public EntityNotFoundException(String message) {
+        super(message);
+    }
+}