`dss` commands can affect any Deployment in the `DSS_NAMESPACE`

### Bug Description

Some implemented `dss` commands can affect any Deployment in the `DSS_NAMESPACE`, not just Notebook deployments.
The list of these commands are:
* `dss stop`
* `dss start`
* `dss logs` (it might be okay that logs can be run with other deployments, but it can be confusing to users so we should revise and discuss that behavior)

came up in [this comment](https://github.com/canonical/data-science-stack/pull/80#discussion_r1572347325)

### To Reproduce

```
pip install -e .
KUBECONFIG=~/.kube/config
dss initialize --kubeconfig $KUBECONFIG
dss stop mlflow --kubeconfig $KUBECONFIG
dss start mlflow --kubeconfig $KUBECONFIG
dss logs mlflow --kubeconfig $KUBECONFIG
```
these commands succeed, where the output should rather be:
```
Failed to [retrieve logs/stop notebook/ start notebook]. Notebook 'mlflow' does not exist.
Run 'dss list' to check all notebooks.
```

### Environment

microk8s 1.28/stable