WIP: Single resource indexing

NOT READY FOR MERGE.

To re-index a single resource, first we have to delete all documents for the resource in the index. That's where most of the work happens. Then we index it as per usual.

This PR adds support for deleting all resource documents in the index:

```GET /index-admin/delete-resource?name=dude&ns=what&id=boom```

That would fire off the job which cascades over multiple taskqueue requests. The id would be the `organization_slug/resource_slug`, the name would be the index name, and the ns is the index namespace.

@tucotuco when you're ready, let's test this out together via code walkthrough, deploy to production, and actual delete.