Allow to register custom categories

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

lib/graphql/resolvers/config.ex

@@ -4,6 +4,7 @@ defmodule Mobilizon.GraphQL.Resolvers.Config do
   """
 
   alias Mobilizon.Config
+  alias Mobilizon.Events.Categories
 
   @doc """
   Gets config.
@@ -57,6 +58,17 @@ defmodule Mobilizon.GraphQL.Resolvers.Config do
     {:ok, %{body_html: body_html, type: type, url: url}}
   end
 
+  @spec event_categories(any(), map(), Absinthe.Resolution.t()) :: {:ok, [map()]}
+  def event_categories(_parent, _args, _resolution) do
+    categories =
+      Categories.list()
+      |> Enum.map(fn %{id: id, label: label} ->
+        %{id: id |> to_string |> String.upcase(), label: label}
+      end)
+
+    {:ok, categories}
+  end
+
   @spec config_cache :: map()
   defp config_cache do
     case Cachex.fetch(:config, "full_config", fn _key ->