Track usage of media files and add a job to clean them

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

lib/mix/tasks/mobilizon/maintenance.ex

@@ -0,0 +1,23 @@
+defmodule Mix.Tasks.Mobilizon.Maintenance do
+  @moduledoc """
+  Tasks to maintain mobilizon
+  """
+
+  use Mix.Task
+
+  alias Mix.Tasks
+  import Mix.Tasks.Mobilizon.Common
+
+  @shortdoc "List common Mobilizon maintenance tasks"
+
+  @impl Mix.Task
+  def run(_) do
+    shell_info("\nAvailable tasks:")
+
+    if mix_shell?() do
+      Tasks.Help.run(["--search", "mobilizon.maintenance."])
+    else
+      show_subtasks_for_module(__MODULE__)
+    end
+  end
+end