Update GCS backend docs for TF >=0.12 (#32065)
Update GCS backend docs for TF >=0.12 (#32065)

* Update gcs.mdx

Updated GCS remote backend to include the >=0.12 remote backend data source formatting (incl .output before output name)

* Update gcs.mdx

removed old data source example

* Update gcs.mdx

updated to local_file and output->outputs

* Update gcs.mdx

removed "outputs" from the pre 0.12 ref
hashicorp/terraform,hashicorp/terraform,hashicorp/terraform