cluster_options Exposing Ability to Include worker/scheduler_extra_pod_labels

As an ability to track resource metrics of the Scheduler and Workers, I would like to put forward a feature request to allow labels to be added to Pods via cluster_options:

```python

options = gateway.cluster_options()
options.extra_pod_labels = {
some_extra_label: label_value,
another_extra_label: another_value
}
```

My main reasoning behind this is to perform more detailed cost analysis for different projects my team is working on. Yes, we can track by user, however, each user may be running workloads for a couple projects at a time.