Add deprecation notice for Stargate in the docs (#1622)

Stargate was already marked as deprecated in the CRD definitions. Reflect the same in the documentation.

Author: DavidLindbom

docs/content/en/components/stargate/_index.md

@@ -9,6 +9,8 @@ Stargate provides a data gateway with REST, GraphQL, and Document APIs in front
 
 If you haven't already installed a K8ssandraCluster using K8ssandra Operator, see the [local install]({{< relref "/install/local" >}}) topic.
 
+**Warning** Stargate is deprecated and does not work with Cassandra 5.0 and newer.
+
 ## Introduction
 
 [Stargate](https://stargate.io) is an open source data gateway that sits between your app and your databases. It brings together an API platform and data request coordination code into one OSS project.