Don't fail the workflow if no statefile is available

[yvrhdn]

Follow up from #22: in a new Terraform workspace when no statefile has been added yet, every speculative run will fail when attempting to fetch the outputs.

We should either:

• fetch the outputs from the statefile that is created by the plan (if this is possible with the API?)
• not fail when the statefile does not exist (i.e. log a warning and do not return any outputs)