LDAP Auth: fix TLS certificate verification

Currently we only support STARTTLS and it was not verifying certificate and hostname correctly. We must pass a custom fqdn_fun/1 function so it knows what value to compare against.

mix.exs

@@ -204,6 +204,7 @@ defmodule Pleroma.Mixfile do
       {:oban_live_dashboard, "~> 0.1.1"},
       {:multipart, "~> 0.4.0", optional: true},
       {:argon2_elixir, "~> 4.0"},
+      {:certifi, "~> 2.12"},
 
       ## dev & test
       {:phoenix_live_reload, "~> 1.3.3", only: :dev},