fix(portal): fix dump config smtp (#6669)

This can cause issue when sockopts is ommited and tls is not used.
Tested with SMTP without and with TLS

cf #6665

elixir/apps/domain/lib/domain/config/definitions.ex

@@ -607,7 +607,7 @@ defmodule Domain.Config.Definitions do
     dump: fn map ->
       Dumper.keyword(map)
       |> Keyword.update(:tls_options, nil, &Dumper.dump_ssl_opts/1)
-      |> Keyword.update(:sockopts, nil, &Dumper.dump_ssl_opts/1)
+      |> Keyword.update(:sockopts, [], &Dumper.dump_ssl_opts/1)
     end
   )