Allow non-etcd backend for k3s (sql, postgres, etc.)

[slickwarren]

Is your feature request related to a problem? Please describe.

all the options related to datastore in this link are to enable non-etcd backend for k3s. This would allow a user to provision a k3s cluster using an externalDB when provisioning through rancher

Describe the solution you'd like

This will require some design discussion, but this would be to allow the user to configure these options through the UI

Describe alternatives you've considered

leave it out of the UI and use the yaml to configure if a user wants to use a non-etcd backend for k3s

Additional context

design discussion required required for k3s GA