Remove Kubernetes example in favor of the Helm chart

[sagikazarmark]

Preflight Checklist

• I agree to follow the Code of Conduct that this project adheres to.
• I have searched the issue tracker for an issue that matches the one I want to file, without success.

Problem Description

There is a Kubernetes example in the repo that needs maintenance from time to time (eg. #2232). We also have an official Helm chart that's the preferred way to install Dex on Kubernetes.

Proposed Solution

Let's get rid of the examples and link to the Helm chart.

We also need better documentation for installing Dex in production.

Alternatives Considered

No response

Additional Information

No response