fastly: use shielding POPs that match backend location

[delroth]

We were previously always shielding via the Virginia POP which is closest to us-east-1. However the S3 buckets for releases.nixos.org and tarballs.nixos.org are hosted in eu-west-1 (Dublin). Let's save on some transatlantic roundtrips, and maybe even improve #212.

[delroth]

  # fastly_service_vcl.nixpkgs-tarballs will be updated in-place
  ~ resource "fastly_service_vcl" "nixpkgs-tarballs" {
      ~ active_version     = 29 -> (known after apply)
      ~ cloned_version     = 29 -> (known after apply)
        id                 = "3z4j8BCi1YqXEqGuwkFn6Q"
        name               = "tarballs.nixos.org"
        # (9 unchanged attributes hidden)

      - backend {
          # At least one attribute in this block is (or was) sensitive,
          # so its contents will not be displayed.
        }
      + backend {
          # At least one attribute in this block is (or was) sensitive,
          # so its contents will not be displayed.
        }

        # (12 unchanged blocks hidden)
    }

  # fastly_service_vcl.releases will be updated in-place
  ~ resource "fastly_service_vcl" "releases" {
      ~ active_version     = 53 -> (known after apply)
      ~ cloned_version     = 53 -> (known after apply)
        id                 = "745rWITBeKgJklfVqQ2Sjb"
        name               = "releases.nixos.org"
        # (8 unchanged attributes hidden)

      - backend {
          # At least one attribute in this block is (or was) sensitive,
          # so its contents will not be displayed.
        }
      + backend {
          # At least one attribute in this block is (or was) sensitive,
          # so its contents will not be displayed.
        }

        # (13 unchanged blocks hidden)
    }

Plan: 0 to add, 2 to change, 0 to destroy.

[delroth]

Apply complete! Resources: 0 added, 2 changed, 0 destroyed.