[GREEN] Add seed_users management command

backend/main/management/commands/seed_users.py

+from django.core.management.base import BaseCommand
+from ...factories import UserFactory
+
+
+class Command(BaseCommand):
+    help = 'Seeds 100 users.'
+
+    def add_arguments(self, parser):
+        parser.add_argument('--size', default=100, type=int)
+
+    def handle(self, *args, **options):
+        size = abs(options['size'])
+        for _ in range(size):
+            u = UserFactory()
+            u.save()
+
+        self.stdout.write(self.style.SUCCESS(f'Successfully seeds {size} users.'))