production users: add Banzai Cloud

Documentation/production-users.md

 # Production users
 
-This document tracks people and use cases for dex in production. [Join the community](https://github.com/dexidp/dex/), and help us keep the list up-to-date.
\ No newline at end of file
+This document tracks people and use cases for dex in production. [Join the community](https://github.com/dexidp/dex/), and help us keep the list up-to-date.
+
+- [Banzai Cloud](https://banzaicloud.com) is using dex for authenticating to its Pipeline control plane and also to authenticate users against provisioned Kubernetes clusters (via Kubernetes OIDC support).