v0.12.0

Remove `count` from stack config data source. Always set `enabled=true` on the `backend` submodule @aknysh (#16)

what

• Remove count from stack config data source
• Always set enabled=true on the backend submodule

why

• count on the data source throws the Terraform "count cannot be computed" error when used from a top-level module which itself uses count on other resources
• Always enable the backend module even if module.this.context sets enabled=false, because we always need to read the remote state (it needs environment and stage from the context) even if a top-level calling module is disabled
  (if we want to set enabled=false on the top-level modules and then use terraform apply to destroy it)