Simple way to add persistent directories

[kkaempf]

Describe the solution you'd like: [A clear and concise description of what you want to happen.]

#1199 shows the current way to add a persistent directory.

This looks complicated and is brittle, as one might miss an essential path.

We should find a way to simply add a path, without affecting any of the 'core' configurations.

Anything else you would like to add: [Miscellaneous information that will assist in solving the issue.]

Environment:

• Elemental release version (use cat /etc/os-release):
• Rancher version:
• Kubernetes version (use kubectl version):
• Cloud provider or hardware configuration:

[davidcassany]

I like the feature request, makes sense to me, but we should be careful with it. I don't think we should use elemental persistent partition to store anything else than Kubernetes and infra related configuration, any application data and storage volumes I believe they should be stored somewhere else, ideally in a different disk/nas. Otherwise redoing or resetting a deployment can be complicated.