chore(#1281): reproducer for parallel access into kafka consumer

added a reproducer for #1281.
indeed the test which is part of the `KafkaEndpointJavaIT` throws:

```shell
java.util.ConcurrentModificationException: KafkaConsumer is not safe for multi-threaded access. currentThread(name: Thread-1, id: 124) otherThread(id: 125)
```

core/citrus-base/src/main/java/org/citrusframework/internal/GitHubIssue.java

@@ -0,0 +1,37 @@
+package org.citrusframework.internal;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.Target;
+
+import static java.lang.annotation.ElementType.METHOD;
+import static java.lang.annotation.ElementType.TYPE;
+import static java.lang.annotation.RetentionPolicy.SOURCE;
+
+/**
+ * Annotation to reference a GitHub issue number associated with a test class or method.
+ * It serves as a linking mechanism between reproducers (tests proving certain behavior) and their corresponding GitHub issues.
+ * <p>
+ * Example usage:
+ * <pre>
+ * {@code @GitHubIssue(1234)
+ * public class MyTest {
+ *     // Class implementation
+ * }
+ *
+ * {@code @GitHubIssue(5678)
+ * public void testMethod() {
+ *     // Method implementation
+ * }}
+ * </pre>
+ */
+@Retention(SOURCE)
+@Target({METHOD, TYPE})
+public @interface GitHubIssue {
+
+    /**
+     * The GitHub issue number to reference.
+     *
+     * @return the issue number in <a href="https://github.com/citrusframework/citrus/issues">the GitHub repository</a>
+     */
+    int value();
+}

endpoints/citrus-kafka/src/main/java/org/citrusframework/kafka/endpoint/KafkaMessageFilteringConsumer.java

@@ -34,13 +34,13 @@
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.ExecutionException;
-import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Future;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.TimeoutException;
 import java.util.function.Function;
 
 import static java.lang.String.format;
+import static java.lang.Thread.currentThread;
 import static java.time.Instant.now;
 import static java.util.Collections.singletonList;
 import static java.util.Objects.isNull;
@@ -140,13 +140,13 @@ public Message receive(String selector, TestContext testContext, long timeout) {
     private List<ConsumerRecord<Object, Object>> findMessageWithTimeout(String topic, long timeout) {
         logger.trace("Applied timeout is {} ms", timeout);
 
-        ExecutorService executorService = newSingleThreadExecutor();
+        var executorService = newSingleThreadExecutor();
         final Future<List<ConsumerRecord<Object, Object>>> handler = executorService.submit(() -> findMessagesSatisfyingMatcher(topic));
 
         try {
             return handler.get(timeout, TimeUnit.MILLISECONDS);
         } catch (InterruptedException e) {
-            Thread.currentThread().interrupt();
+            currentThread().interrupt();
             throw new CitrusRuntimeException("Thread was interrupted while waiting for Kafka message", e);
         } catch (ExecutionException e) {
             throw new CitrusRuntimeException(format("Failed to receive message on Kafka topic '%s'", topic), e);
@@ -157,8 +157,8 @@ private List<ConsumerRecord<Object, Object>> findMessageWithTimeout(String topic
 
             throw new MessageTimeoutException(timeout, topic, e);
         } finally {
-            executorService.shutdownNow();
             consumer.unsubscribe();
+            executorService.shutdownNow();
         }
     }
 

endpoints/citrus-kafka/src/test/java/org/citrusframework/kafka/integration/KafkaEndpointJavaIT.java

@@ -20,6 +20,7 @@
 import org.citrusframework.annotations.CitrusTest;
 import org.citrusframework.exceptions.CitrusRuntimeException;
 import org.citrusframework.exceptions.TestCaseFailedException;
+import org.citrusframework.internal.GitHubIssue;
 import org.citrusframework.kafka.endpoint.KafkaEndpoint;
 import org.citrusframework.kafka.endpoint.selector.KafkaMessageByHeaderSelector;
 import org.citrusframework.kafka.message.KafkaMessage;
@@ -33,6 +34,7 @@
 import static org.citrusframework.actions.ReceiveMessageAction.Builder.receive;
 import static org.citrusframework.actions.SendMessageAction.Builder.send;
 import static org.citrusframework.actions.SleepAction.Builder.sleep;
+import static org.citrusframework.container.Parallel.Builder.parallel;
 import static org.citrusframework.kafka.endpoint.KafkaMessageFilter.kafkaMessageFilter;
 import static org.citrusframework.kafka.endpoint.selector.KafkaMessageByHeaderSelector.ValueMatchingStrategy.ENDS_WITH;
 import static org.citrusframework.kafka.endpoint.selector.KafkaMessageByHeaderSelector.ValueMatchingStrategy.STARTS_WITH;
@@ -274,4 +276,35 @@ public void findKafkaEvent_headerEquals_java_DSL() {
         );
     }
 
+    @CitrusTest
+    @GitHubIssue(1281)
+    public void parallel_access_thread_safety() {
+        var body = "parallel_access_thread_safety";
+
+        var key = "Name";
+
+        var brother1 = "Elladan";
+        var brother2 = "Elrohir";
+
+        when(
+                send(kafkaWithRandomConsumerGroupEndpoint)
+                        .message(new KafkaMessage(body).setHeader(key, brother1))
+        );
+
+        when(
+                send(kafkaWithRandomConsumerGroupEndpoint)
+                        .message(new KafkaMessage(body).setHeader(key, brother2))
+        );
+
+
+        then(
+                parallel()
+                        .actions(
+                                kafkaWithRandomConsumerGroupEndpoint.findKafkaEventHeaderEquals(Duration.ofSeconds(1L), key, brother1)
+                                        .body(body),
+                                kafkaWithRandomConsumerGroupEndpoint.findKafkaEventHeaderEquals(Duration.ofSeconds(1L), key, brother2)
+                                        .body(body)
+                        )
+        );
+    }
 }