Allow %cancel_load magic to cancel all queued jobs

[triggan]

Is your feature request related to a problem? Please describe. If a user submits multiple queued bulk load jobs, there is no other way to cancel these other than to issue multiple HTTP DELETE requests (one for each bulk load job), or to issue a %cancel_load magic call for each bulk load request. Finding the bulk load jobs that are queued can also be difficult, as a user would need to fetch all bulk load job IDs and iterate across all of them to find the jobs that are currently in LOAD_IN_QUEUE status.

Describe the solution you'd like Add a --all-in-queue flag to the %cancel_load magic. This would automatically perform the steps above for a user and clear out the entire bulk load job queue.

Describe alternatives you've considered An alternative would be to add this functionality directly into the Neptune control plane / /loader API. However, implementing this in the notebooks would be an easier first implementation. This same functionality could be pushed to the /loader API in a future time.

Additional context N/A