GH-3020 Make Kotlin dependency optional

Resolves #3020

Author: olegz

core/spring-cloud-stream/pom.xml

@@ -89,10 +89,12 @@
         <dependency>
             <groupId>org.jetbrains.kotlin</groupId>
             <artifactId>kotlin-stdlib-jdk8</artifactId>
+            <optional>true</optional>
         </dependency>
 		<dependency>
 			<groupId>com.fasterxml.jackson.datatype</groupId>
 			<artifactId>jackson-datatype-jsr310</artifactId>
+			<optional>true</optional>
 		</dependency>
     </dependencies>