Set users as applicants upon registration

In preparation for the new login style, defaulting new users to applicants was replaced by assigning the user to the group when they submit an application. This was done in the clean_submission code which was removed by us (for reasons lost to the annals of time).

So now, users were never getting assigned applicant, which prevented them from doing applicant things (like viewing the dashboard). In order to repair, we added back in the code in user creation, however in the future we will need to figure out how to bring this logic more in line with how upstream does it now.

Issue ots/clients/ardc/hypha-tracker#296: New Users do not automatically recieve applicant role after activating account

merging now as we need this in staging :)