Update the Oban Dashboard to show only for admin users.

lib/decentralised_book_index_web/plugs/require_admin.ex

@@ -0,0 +1,21 @@
+defmodule DecentralisedBookIndexWeb.Plugs.RequireAdmin do
+  import Plug.Conn
+  import Phoenix.Controller
+
+  alias DecentralisedBookIndex.Accounts.Role
+
+  def init(default), do: default
+
+  def call(conn, _opts) do
+    current_user = conn.assigns[:current_user]
+
+    if current_user && Role.can_administrate?(current_user.role) do
+      conn
+    else
+      conn
+      |> put_flash(:error, "Unauthorized")
+      |> redirect(to: "/")
+      |> halt()
+    end
+  end
+end