Fix load SECRET_KEY from correct file

Before: everyone was using same hardcoded SECRED_KEY
Enduser will need to run 'python manage.py setclusters clusters.yaml'
again.

Signed-off-by: Justin Cinkelj <justin.cinkelj@xlab.si>

Author: justinc1

setup/collections/ansible_collections/ansible/containerized_installer/roles/automationdashboard/templates/django_dashboard_conf.py.j2

@@ -1,3 +1,6 @@
+with open("/etc/dashboard/SECRET_KEY") as fin:
+    SECRET_KEY = fin.read()
+
 ALLOWED_HOSTS=["*"]
 CORS_ALLOWED_ORIGINS = [
     "http://localhost:8080",