Export participants to different formats

* CSV
* PDF (requires Python dependency `weasyprint`)
* ODS (requires Python dependency `pyexcel_ods3`)

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

lib/graphql/schema/config.ex

@@ -65,6 +65,8 @@ defmodule Mobilizon.GraphQL.Schema.ConfigType do
     field(:auth, :auth, description: "The instance auth methods")
     field(:instance_feeds, :instance_feeds, description: "The instance's feed settings")
     field(:web_push, :web_push, description: "Web Push settings for the instance")
+
+    field(:export_formats, :export_formats, description: "The instance list of export formats")
   end
 
   @desc """
@@ -307,6 +309,15 @@ defmodule Mobilizon.GraphQL.Schema.ConfigType do
     field(:public_key, :string, description: "The server's public WebPush VAPID key")
   end
 
+  @desc """
+  Export formats configuration
+  """
+  object :export_formats do
+    field(:event_participants, list_of(:string),
+      description: "The list of formats the event participants can be exported to"
+    )
+  end
+
   object :config_queries do
     @desc "Get the instance config"
     field :config, :config do