Fix Cassandra init script execution

The script file may have several DDL expression to execute.
They probably have to be called one-by-one as they are declared.
For example our `init-db.cql` has DDL to delete table and the next to create.

* Fix `CassandraAppClusterConfiguration.keyspaceInitializer()`
to use a `Flux.concatMap()` instead of `flatMap()` to ensure sequential
items processing in the order they appear upstream

consumer/cassandra-consumer/src/main/java/org/springframework/cloud/fn/consumer/cassandra/cluster/CassandraAppClusterConfiguration.java

@@ -123,7 +123,7 @@ public class CassandraAppClusterConfiguration {
 
 		Flux.fromArray(StringUtils.delimitedListToStringArray(scripts, ";", "\r\n\f"))
 				.filter(StringUtils::hasText) // an empty String after the last ';'
-				.flatMap(script -> reactiveCqlOperations.execute(script + ";"))
+				.concatMap(script -> reactiveCqlOperations.execute(script + ";"))
 				.blockLast();
 
 		return null;