Rename global tfvars file in FAST

[ludoo]

Terraform variable order uses lexical ordering, from which follows that overriding definitions in the FAST globals.auto.tfvars.json file becomes a trial and error process.

Renaming it to 0-globals.auto.tfvars.json would

• allow easy override via properly name files from later stages (to e.g. override prefix in a stage 3)
• clearly mark it as being output from stage 0