management: Use required kwargs in add_realm_args.

This makes management commands more readable, since one doesn't need
to know details of how the library works to read based code.

zerver/management/commands/scrub_realm.py

@@ -9,7 +9,7 @@ class Command(ZulipBaseCommand):
     help = """Script to scrub a deactivated realm."""
 
     def add_arguments(self, parser: ArgumentParser) -> None:
-        self.add_realm_args(parser, True)
+        self.add_realm_args(parser, required=True)
 
     def handle(self, *args: Any, **options: str) -> None:
         realm = self.get_realm(options)