ADOPTERS: replace Documentation/production-users.md, add Chef

Signed-off-by: Stephan Renatus <srenatus@chef.io>

ADOPTERS.md

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+# Adopters
+
+This is a list of production adopters of Dex (in alphabetical order):
+
+- [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).
+- [Chef](https://chef.io) uses Dex for authenticating users in [Chef Automate](https://automate.chef.io/). The code is Open Source, available at [`github.com/chef/automate`](https://github.com/chef/automate).

Documentation/production-users.md

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-# 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.
-
-- [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).