remove rejected preprint version (#11693)

## Ticket
* https://openscience.atlassian.net/browse/ENG-10368

## Purpose
Add Delete preprint function for rejected preprints

## Changes
add BE option for `rejected` preprint removal 

related FE changings are in the PR CenterForOpenScience/angular-osf#940

(suppose will be needed to add 'rejected' not 'draft' for UI depending status in another one ticket maybe)

Author: mkovalua

api/preprints/views.py

@@ -350,7 +350,7 @@ def get_parser_context(self, http_request):
         return res
 
     def delete(self, request, *args, **kwargs):
-        if self.get_preprint().machine_state == 'initial':
+        if self.get_preprint().machine_state in ['initial', 'rejected']:
             return super().delete(request, *args, **kwargs)
 
         raise ValidationError('You cannot delete created preprint')