added calendar slot_duration config (#989)

src/Configuration/CalendarConfiguration.php

@@ -97,4 +97,9 @@ class CalendarConfiguration implements SystemBundleConfiguration
     {
         return $this->find('google.sources');
     }
+
+    public function getSlotDuration(): string
+    {
+        return (string) $this->find('slot_duration');
+    }
 }

src/DependencyInjection/Configuration.php

@@ -250,6 +250,7 @@ class Configuration implements ConfigurationInterface
             ->children()
                 ->booleanNode('week_numbers')->defaultTrue()->end()
                 ->integerNode('day_limit')->defaultValue(4)->end()
+                ->scalarNode('slot_duration')->defaultValue('00:30:00')->end()
                 ->arrayNode('businessHours')
                     ->addDefaultsIfNotSet()
                     ->children()