Sets the VM your agent pool will run on. Valid values are: S1 (2 vCPUs, 3 GiB RAM), S2 (4 vCPUs, 8 GiB RAM), S3 (8 vCPUs, 16 GiB RAM) or I6 (64 vCPUs, 216 GiB RAM, Isolated). Defaults to S1. Changing this forces a new Azure Container Registry Agent Pool to be created.