Consider increasing DATA_UPLOAD_MAX_NUMBER_FIELDS setting

[evansd]

There turns out to be another barrier to dispatching a large number of jobs which is that by default Django won't accept more than 1,000 checkbox inputs and will throw a TooManyFieldsSent error.

Em hit this error recently (presumably as a result of using my hacky JS thing to select a lot of checkboxes):
https://ebm-datalab.sentry.io/issues/6090198345/

The Django docs suggest that "applications that are expected to receive an unusually large number of form fields should tune this setting." I think it would be reasonable to increase it, maybe to a couple of thousand. Because of the existence of "run all" it doesn't act as a hard barrier to prevent users from dispatching too many jobs in any case.