make th first option default and put gpus at the end of the list

Author: GeorgianaElena

config/clusters/aimatx-2i2c-hub/common.values.yaml

@@ -65,6 +65,7 @@ jupyterhub:
             mem_15_gb:
               display_name: ~15 GB RAM, ~1.8 CPUs
               description: Up to ~4 CPUs when available
+              default: true
               kubespawner_override:
                 mem_guarantee: 15611359038
                 mem_limit: 15611359038
@@ -122,7 +123,7 @@ jupyterhub:
                 cpu_limit: 62.575
                 node_selector:
                   node.kubernetes.io/instance-type: r5.16xlarge
-            gpu:
+            n_gpu:
               display_name: NVIDIA Tesla T4, ~16 GB, ~4 CPUs
               description: Start a container on a dedicated node with a GPU
               kubespawner_override: