chore: add missing topic examples for injection in CodeBlocks

examples/topic/src/main/java/momento/client/doc_examples/DocExamplesJavaAPIs.java

@@ -0,0 +1,79 @@
+package momento.client.doc_examples;
+
+import momento.sdk.ISubscriptionCallbacks;
+import momento.sdk.TopicClient;
+import momento.sdk.auth.CredentialProvider;
+import momento.sdk.config.TopicConfigurations;
+import momento.sdk.responses.topic.TopicMessage;
+import momento.sdk.responses.topic.TopicPublishResponse;
+import momento.sdk.responses.topic.TopicSubscribeResponse;
+
+public class DocExamplesJavaAPIs {
+
+  @SuppressWarnings("EmptyTryBlock")
+  public static void example_API_InstantiateTopicClient() {
+    try (final TopicClient topicClient =
+        new TopicClient(
+            CredentialProvider.fromEnvVar("MOMENTO_API_KEY"),
+            TopicConfigurations.Laptop.latest())) {
+      // ...
+    }
+  }
+
+  public static void example_API_TopicSubscribe(TopicClient topicClient) {
+    final TopicSubscribeResponse topicSubscribeResponse =
+        topicClient
+            .subscribe(
+                "test-cache",
+                "test-topic",
+                new ISubscriptionCallbacks() {
+                  @Override
+                  public void onItem(TopicMessage message) {
+                    System.out.println("Received message on 'test-topic': " + message.toString());
+                  }
+
+                  @Override
+                  public void onError(Throwable error) {
+                    System.err.println(
+                        "Error: Subscription to 'test-topic' failed. Details: "
+                            + error.getMessage());
+                  }
+
+                  @Override
+                  public void onCompleted() {
+                    System.out.println("Subscription to 'test-topic' completed");
+                  }
+                })
+            .join();
+
+    if (topicSubscribeResponse instanceof TopicSubscribeResponse.Error error) {
+      throw new RuntimeException(
+          "An error occurred while attempting to subscribe to topic 'test-topic': "
+              + error.getErrorCode(),
+          error);
+    }
+  }
+
+  public static void example_API_TopicPublish(TopicClient topicClient, String message) {
+    final TopicPublishResponse publishResponse =
+        topicClient.publish("test-cache", "test-topic", message).join();
+    if (publishResponse instanceof TopicPublishResponse.Error error) {
+      throw new RuntimeException(
+          "An error occurred reading messages from topic 'test-topic':" + error.getErrorCode(),
+          error);
+    }
+  }
+
+  public static void main(String[] args) {
+    example_API_InstantiateTopicClient();
+
+    try (final TopicClient topicClient =
+        new TopicClient(
+            CredentialProvider.fromEnvVar("MOMENTO_API_KEY"),
+            TopicConfigurations.Laptop.latest())) {
+
+      example_API_TopicSubscribe(topicClient);
+      example_API_TopicPublish(topicClient, "Hello world");
+    }
+  }
+}