KFT improvements

- Pass env as secret instead 
- Checkpointing (write about just-in-time checkpointing)
- - Create PVC first (has to be RWX, 3.4 for S3 instead) and attach it
- - Add a second job in the notebook to pre-empt the current job to show checkpointing?
- UI and progress checking (GA in 3.3 (maybe?))
- Rename from "Kubeflow Training Operator (KFTO v1)" to "Kubeflow Trainer (KFT v2)"