feat: Add Service Stub Pattern using Sentiment Analysis example (#3215)

* Add Service Stub Pattern using Sentiment Analysis example

* Fix Checkstyle issues

* Suppress Sonar warning for Random usage in RealSentimentAnalysisServer

service-stub/src/main/java/com/iluwatar/servicestub/SentimentAnalysisServer.java

@@ -0,0 +1,15 @@
+package com.iluwatar.servicestub;
+
+/**
+ * Sentiment analysis server interface to be implemented by sentiment analysis services.
+ */
+
+public interface SentimentAnalysisServer {
+  /**
+   * Analyzes the sentiment of the input text and returns the result.
+   *
+   * @param text the input text to analyze
+   * @return sentiment classification result
+   */
+  String analyzeSentiment(String text);
+}