Revisit ARC for container based runners

[afrittoli]

We discussed in a previous WG to revisit ARC

• Start with a small deployment
• Migrate simple jobs incrementally (no Docker, no GPU to begin with)

[zxiiro]

We can reuse the pytorch/ci-infra repo for this work, the existing "arc" folder was for the previous attempt, maybe we can rename it to something like "arc-old" or something to preserve the old deployment and create a fresh attempt with a new "arc" folder. ci-infra is already configured with everything it needs to run Terraform.

[zxiiro]

We may need to adjust the existing ARC workflow GHA depending on how we want to structure the new Terraform.