Add ability to generate tokens in bulk

[ezekg]

Once we tackle #314, we'll need a way to generate multiple tokens at one time, up to hundreds of tokens. I think adding a bulk token generation endpoint may be a good call here. It could kick off a job that generates x number of tokens. We would need to offer some sort of system where the user can track the job's progress, such as using an Accepted HTTP response status, and then providing a Location header detailing where the job's progress can be polled.