delete files from storage

It would be helpful to have a command in the CLI to delete files (or a set of files under a specific path). During development, I'd like to reset user and app generated data in both Firestore and Storage

The related firestore command is:
```
firebase firestore:delete -r -y items/subcollection
```

I would like a command like:

```
firebase storage:delete -r -y products/images
```

Workaround:
it looks like this is available in `gsutil`

To delete everything in the default storage bucket under `product/images`:
``
gsutil rm gs://$PROJECT_ID.appspot.com/product/images/*
``
docs: https://cloud.google.com/storage/docs/gsutil/commands/rm