Add Goldstack Terraform state #24

Running infra commands is not as fast as it could be due to the need for Goldstack to run an init before every operation, as well as to switch to the correct workspace.

This could be mitigated by having a goldstack-tfstate.json in the infra/ folder that is not checked into source control.

It is further at the moment not easy to upgrade to a newer Terraform version, especially for all modules. Goldstack could add a file goldstack-tfconfig.json that contains the Terraform version used by the current module. This allows upgrading the modules to a new TF version one by one.