Mention useful on-premise tools

[rmarquis]

For people that want to go beyond the cloud solution we propose,
mention some useful tools that can be used on-premise and add links in the 'Tools" page:

• cncf landscape: https://landscape.cncf.io/ (filter "graduated")
• kubespray (deployment k8s), argo (management and continuous k8s deployment), harbor (container registry), helm (for argo and git integration, needed for GitLab actions too), maybe Docker Swarm (simplified cluster), docker registry (local registry)?