[Docs] Guide the user to use openssl to create CSR for X509 auth

**What would you like to be added**:

I would like to create one section guiding the user to use X509 cert auth for Kubernetes API auth.

In other words, the EKS-A version for the docs:
https://docs.aws.amazon.com/eks/latest/userguide/eks-outposts-network-disconnects.html

Changes are needed for the step 8 and later.

**Why is this needed**:

The customer would like to have details guides to managed access of EKS-A without external OIDC provider.

Start with the linked AWS EKS Outposts guide and review the steps from step 8 onward. Add an EKS-A documentation section explaining how to use openssl to create a CSR for X509 Kubernetes API authentication and manage access without an external OIDC provider; the guide is done when those steps are covered clearly.

Written by the indexing model from the issue text.