Remove managed k8s tutorials (EKS, AKS, GKE) and consolidate content on cloud pre-reqs page

We currently have individual tutorials for setting up managed Kubernetes services:

AKS - https://docs.couchbase.com/operator/current/tutorial-aks.html

EKS - https://docs.couchbase.com/operator/current/tutorial-eks.html

GKE - https://docs.couchbase.com/operator/current/tutorial-gke.html

These tutorials are not consistent with each other content-wise. For example, one of the tutorials may walk you through setting up a k8s cluster while another will assume you have already done this task beforehand. The AKS and GKE tutorials go as far as providing commands for deploying the k8s cluster itself. These commands include the k8s version which quickly becomes out of date (see DOC-7693).

These tutorials on their own don't fully serve any purpose. They don't provide enough hand-holding to help a k8s newbie set up a full k8s cluster and Operator deployment, but they also have a lot of noise in them that makes them difficult/annoying for an advanced user to use.

In general, we should move away from describing how to set up a k8s cluster within these managed services, unless we choose to do a more substantial tutorial that walks you through a full deployment of both the k8s cluster and the Operator.

At this time, we should take the relevant content from these tutorials and move it to the Public Cloud Prerequisites page: https://docs.couchbase.com/operator/current/prerequisite-cloud.html