Add guide to setup remote access to private networks

[gdemonet]

Component: docs

Why this is needed:

Recommended architectures use private networks for the cluster control and workload planes. By definition, the host will need some form of setup to access these networks (e.g. using a VPN).

What should be done:

Since accessing cluster services from the user's host is a common task, it would make sense to provide minimal guidance on how to setup such a VPN in various contexts (with a well-known cloud provider, using OpenStack routers, on bare-metal with sshuttle, ...).

[NicolasT]

I disagree.

Whilst we can document something in scope of e.g., running a test cluster on OpenStack, then explaining how to access such 'private networks', I don't think documenting something in general is right: the networks used for control-plane and workload-plane are existing networks in a datacenter in which a cluster is deployed, and how to access these networks depends 100% on the datacenter network topology and such. However, we can expect that any node which needs access to some service provided by the cluster (this may be an administrator's machine accessing the control-plane network, or some application servers accessing services on the workload-plane) is already in place (using whatever relevant means).

So, if the scope of this request is dev/test environments on e.g., OpenStack, then sure, in the 'developer guide'. Not in the end-user docs.

[gdemonet]

Fair point, could be part of the contrib/terraform/README for a start, and maybe also add a section for this in the developer docs.