Add `Waiting for gpu` state to `dss list`

### Why it needs to get done

In kubernetes is not possible to share a single GPU between pods. because of these when we try to create two gpu backed notebooks the latter one will go to Pending state with status of `Insufficient resources ...`. There can be only one active Pod at a time using the single GPU in the computer.

Because of this we want to introduce a state `Waiting for gpu` in `dss list`. To recover from this state user can stop the notebook currently using the GPU. This will cause that the next notebook will get the gpu assigned.

### What needs to get done

Add `Waiting for gpu` state to `dss list` which indicates that the notebook is trying to allocate gpu resource but there are currently no available.

### When is the task considered done

dss list is supporting this state