Make CompletionStageFunction public and rename package for classes un…

…der the new library module (removing 'javaagent' from the package path)

instrumentation/cassandra/cassandra-4.0/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/cassandra/v4_0/CompletionStageFunction.java

@@ -8,7 +8,7 @@
 import com.datastax.oss.driver.api.core.CqlSession;
 import java.util.function.Function;
 
-public class CompletionStageFunction implements Function<Object, Object> {
+public class CompletionStageFunctions implements Function<Object, Object> {
 
   @Override
   public Object apply(Object session) {