feat(config): add durationOfLongEvent in FullConfig query

For #1568

lib/graphql/resolvers/config.ex

@@ -94,6 +94,7 @@ defmodule Mobilizon.GraphQL.Resolvers.Config do
       contact: Config.contact(),
       demo_mode: Config.instance_demo_mode?(),
       long_events: Config.instance_long_events?(),
+      duration_of_long_event: Config.instance_duration_of_long_event(),
       description: Config.instance_description(),
       long_description: Config.instance_long_description(),
       slogan: Config.instance_slogan(),

lib/graphql/schema/config.ex

@@ -32,6 +32,11 @@ defmodule Mobilizon.GraphQL.Schema.ConfigType do
 
     field(:demo_mode, :boolean, description: "Whether the demo mode is enabled")
     field(:long_events, :boolean, description: "Whether the long events mode is enabled")
+
+    field(:duration_of_long_event, :integer,
+      description: "Events longer than this duration are considered long events"
+    )
+
     field(:country_code, :string, description: "The country code from the IP")
     field(:location, :lonlat, description: "The IP's location")
     field(:geocoding, :geocoding, description: "The instance's geocoding settings")