Extract StaticAssets hook with a single default live_session

lib/music_library_web/hooks/static_assets.ex

@@ -0,0 +1,14 @@
+defmodule MusicLibraryWeb.Hooks.StaticAssets do
+  use MusicLibraryWeb, :live_component
+
+  def on_mount(:default, _params, _session, socket) do
+    socket =
+      if static_changed?(socket) do
+        put_flash(socket, :warning, gettext("The application has been updated, please reload."))
+      else
+        socket
+      end
+
+    {:cont, socket}
+  end
+end