Postpone SECRET_KEY evaluation to the qcluster command execution (#332)

* Suppress ImproperlyConfigured within Conf, allowing the exception to be raised specifically during the 'qcluster' command instead.

This ensures build scripts and workflows can freely execute other Django commands (e.g., 'python manage.py collectstatic') without failing due to a missing/empty secret key.

* Closes #279

Co-authored-by: Tug of Peas <19413623+tugofpeas@users.noreply.github.com>

django_q/management/commands/qcluster.py

@@ -1,5 +1,6 @@
 import os
 
+from django.conf import settings
 from django.core.management.base import BaseCommand
 from django.utils.translation import gettext as _
 
@@ -28,6 +29,8 @@ class Command(BaseCommand):
         )
 
     def handle(self, *args, **options):
+        # Ensure that the cluster starts only if the SECRET_KEY is set, as it is required for signing.
+        settings.SECRET_KEY
         # Set alternative cluster_name before creating the cluster (cluster_name is broker's queue_name, too)
         cluster_name = options.get("cluster_name")
         if cluster_name: