fix(participant exports): fix participants by returning the export type as well as the file path

We previously used the Apollo context but that's really unreliable.

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

lib/graphql/resolvers/participant.ex

@@ -302,7 +302,7 @@ defmodule Mobilizon.GraphQL.Resolvers.Participant do
         if can_event_be_updated_by?(event, moderator_actor) do
           case export_format(format, event, roles, locale) do
             {:ok, path} ->
-              {:ok, path}
+              {:ok, %{path: path, format: format}}
 
             {:error, :export_dependency_not_installed} ->
               {:error,