Security recommendation/hardening guide for applications that use Kubernetes client

[AnshumanTripathi]

Create a security recommendation/hardening guide for applications that use the Kubernetes client. This could include different use-cases like:

1. Creating an application which runs kubectl commands.
2. An application that uses the Kubernetes client
3. A Kubernetes Operator

Issue cloned from SIG Security - https://github.com/kubernetes/sig-security/issues/121

Relates to - https://github.com/kubernetes/website/pull/46326

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[sftim]

/language en /kind feature /sig security docs

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