Add Audiobookshelf Deployment in Kubernetes Documentation

[mvinkarklins]

Pull Request Description:

This PR adds documentation for deploying Audiobookshelf in a Kubernetes cluster using NGINX as the ingress controller and Let's Encrypt for certificate management. The following are included in this update:

• Prerequisites section to guide users on setting up the Kubernetes cluster, NGINX ingress controller, and Let's Encrypt ClusterIssuer.
• Namespace creation for the Audiobookshelf deployment.
• Kubernetes manifest for the Audiobookshelf Service, Ingress, and Deployment, including necessary volumes for audiobooks, podcasts, config, and metadata storage.
• Instructions on how to apply the manifests and verify the deployment in Kubernetes.

This documentation ensures that users can easily deploy Audiobookshelf in a Kubernetes environment with automated TLS certificates using Cert-Manager and Let's Encrypt.

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[mvinkarklins]

Let me know if you have any feedback! 💡