lysgraf: use lookup function to get hiera value

manifests/init.pp

@@ -323,7 +323,7 @@ class lysgraf {
         name                 => 'Keycloak-OAuth',
         allow_sign_up        => true,
         client_id            => 'grafana-oauth',
-        #client_secret        => Sensitive(chomp($client_secret_content)),
+        client_secret        => Sensitive(chomp(lookup('lysgraf::grafana::client_secret_content'))),
         scopes               => 'openid email profile offline_access roles',
         email_attribute_path => 'email',
         login_attribute_path => 'username',