Add Kubernets deployments to the how to scale page

[patriknw]

When we have the deployment story ready we should describe that each Akka Cluster role should correspond to a Kubernetes deployment so the roles can be scaled by scaling the pods. Still one Akka Cluster.

[ignasi35]

In order to have dedicated nodes on an Akka Cluster it is necessary to create different Deployment's. Each Deployment will use its ReplicaSet but all the Deployment's must use the same label. Cluster bootstrap, then, uses that label so pods from different replicasets can locate each other. Finally, the service selector uses that same label.

Creating custom Deployment's for each type of node introduces a lot of duplicity since the two yml are identical except for a few settings. This is a use case where kustomize, helm or other tools to regenerate the YML would be of help.

I did some experiments in https://github.com/ignasi35/deployment-experiments/commit/f6478b85ac70b40d49a76b8a391b50b385061177