add "only platform admin can create groups" and "only groups can create events" restrictions

config/config.exs

@@ -40,9 +40,11 @@ config :mobilizon, :instance,
   email_reply_to: "noreply@localhost"
 
 config :mobilizon, :groups, enabled: true
-
 config :mobilizon, :events, creation: true
 
+config :mobilizon, :restrictions, only_admin_can_create_groups: false
+config :mobilizon, :restrictions, only_groups_can_create_events: false
+
 # Configures the endpoint
 config :mobilizon, Mobilizon.Web.Endpoint,
   url: [