docs: fix operator list in tutorials section (#696)

* docs: fix operator list in tutorials section

* Update modules/tutorials/pages/index.adoc

Co-authored-by: Sebastian Bernauer <sebastian.bernauer@stackable.de>

---------

Co-authored-by: Sebastian Bernauer <sebastian.bernauer@stackable.de>

Author: xeniape

modules/tutorials/pages/index.adoc

@@ -17,10 +17,10 @@ Follow any of these guides to get started with a specific product.
 * xref:druid:getting_started/index.adoc[Stackable Operator for Apache Druid]
 * xref:hbase:getting_started/index.adoc[Stackable Operator for Apache HBase]
 * xref:hdfs:getting_started/index.adoc[Stackable Operator for Apache HDFS]
-* xref:druid:getting_started/index.adoc[Stackable Operator for Apache Druid]
 * xref:hive:getting_started/index.adoc[Stackable Operator for Apache Hive]
 * xref:kafka:getting_started/index.adoc[Stackable Operator for Apache Kafka]
 * xref:nifi:getting_started/index.adoc[Stackable Operator for Apache NiFi]
+* xref:opa:getting_started/index.adoc[Stackable Operator for OpenPolicyAgent]
 * xref:spark-k8s:getting_started/index.adoc[Stackable Operator for Apache Spark]
 * xref:superset:getting_started/index.adoc[Stackable Operator for Apache Superset]
 * xref:trino:getting_started/index.adoc[Stackable Operator for Trino]