Fix digest email processing, consolidate Oban queues

The email related jobs can all share a single Oban queue

priv/repo/migrations/20231107200724_consolidate_email_queues.exs

@@ -0,0 +1,9 @@
+defmodule Pleroma.Repo.Migrations.ConsolidateEmailQueues do
+  use Ecto.Migration
+
+  def change do
+    execute(
+      "UPDATE oban_jobs SET queue = 'mailer' WHERE queue in ('digest_emails', 'new_users_digest')"
+    )
+  end
+end