Alter priority of Delete activities to be lowest

This will prevent a user with a large number of posts from negatively affecting performance of the outgoing federation queue if they delete their account.

lib/pleroma/web/activity_pub/side_effects.ex

@@ -282,7 +282,6 @@ defmodule Pleroma.Web.ActivityPub.SideEffects do
   # Tasks this handles:
   # - Delete and unpins the create activity
   # - Replace object with Tombstone
-  # - Set up notification
   # - Reduce the user note count
   # - Reduce the reply count
   # - Stream out the activity

lib/pleroma/web/federator.ex

@@ -47,10 +47,15 @@ defmodule Pleroma.Web.Federator do
   end
 
   @impl true
-  def publish(activity) do
-    PublisherWorker.enqueue("publish", %{"activity_id" => activity.id})
+  def publish(%Pleroma.Activity{data: %{"type" => type}} = activity) do
+    PublisherWorker.enqueue("publish", %{"activity_id" => activity.id},
+      priority: publish_priority(type)
+    )
   end
 
+  defp publish_priority("Delete"), do: 3
+  defp publish_priority(_), do: 0
+
   # Job Worker Callbacks
 
   @spec perform(atom(), module(), any()) :: {:ok, any()} | {:error, any()}