Target ring1 machines in prod gateway deploys (#151)

prod/variables.sh left GATEWAY_RINGS unset, so it defaulted to ring0 and
the prod deploy pipeline skipped every ring1-tagged machine. Set
GATEWAY_RINGS="ring1" so production gateways are actually deployed to.

Author: carlosmartinez

infrastructure/environments/prod/variables.sh

@@ -2,9 +2,10 @@ ENV_CONFIG=prod
 ENVIRONMENT=prod
 AZURE_SUBSCRIPTION="Breast Screening - Manage Breast Screening - Prod"
 HUB_SUBSCRIPTION="Digital Screening DToS - Core Services Prod Hub"
-HUB=prod
 TERRAFORM_MODULES_REF=main
+HUB=prod
 ENABLE_SOFT_DELETE=true
 ADO_MANAGEMENT_POOL=private-pool-prod-uks
 CLOUD_API_HOSTNAME=manage-breast-screening.nhs.uk
-# To onboard more rings: set GATEWAY_RINGS="ring0 ring1 ring2 ..." in this file
+# ring1 = first real sites (one per PACS vendor)
+GATEWAY_RINGS="ring1"