fix: examples/kotlin-greeter-service/pom.xml to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JAVA-ORGJETBRAINSKOTLIN-2393744

examples/kotlin-greeter-service/pom.xml

@@ -11,7 +11,7 @@
     <artifactId>kotlin-greeter-service</artifactId>
 
     <properties>
-        <kotlin.version>1.9.22</kotlin.version>
+        <kotlin.version>2.1.0</kotlin.version>
         <main.class>GreeterServiceKt</main.class>
     </properties>