tests: validate that plan work with ReadOnly permissions

[Codelax]

Given an APIKey with AllProductsReadOnly as only permission set.

It would be expected that all resources' state can be read using this API key.
This would allow to do terraform plan with this key in a CI or fetch the current state.

As an example, k8s_cluster require more permissions as it tries to fetch kubeconfig on each Read

How can this be achieved ?
We can update simple tests to include a PlanOnly step. This step should be executed using a ReadOnly key.