[FLINK-19001] Add flink-clients to the example pom.xml

Since the move to 1.11, Flink executors are refactored
out of flink-streaming-java and moved into flink-clients
which is a required dependency now.
diff --git a/statefun-examples/statefun-flink-datastream-example/pom.xml b/statefun-examples/statefun-flink-datastream-example/pom.xml
index edd09ca..d08a1dc 100644
--- a/statefun-examples/statefun-flink-datastream-example/pom.xml
+++ b/statefun-examples/statefun-flink-datastream-example/pom.xml
@@ -33,7 +33,6 @@
             <artifactId>statefun-flink-datastream</artifactId>
             <version>${project.version}</version>
         </dependency>
-
         <dependency>
             <groupId>org.apache.flink</groupId>
             <artifactId>flink-streaming-java_${scala.binary.version}</artifactId>
@@ -49,6 +48,20 @@
             </exclusions>
         </dependency>
         <dependency>
+            <groupId>org.apache.flink</groupId>
+            <artifactId>flink-clients_${scala.binary.version}</artifactId>
+            <version>${flink.version}</version>
+            <exclusions>
+                <!-- The following exclusion is needed since this artifacts pulls two different versions
+                     of slf4j, and thus failing the maven convergence plugging.
+                 -->
+                <exclusion>
+                    <groupId>org.slf4j</groupId>
+                    <artifactId>slf4j-api</artifactId>
+                </exclusion>
+            </exclusions>
+        </dependency>
+        <dependency>
             <groupId>org.slf4j</groupId>
             <artifactId>slf4j-api</artifactId>
             <version>1.7.25</version>