Conversations: Add a function to 'import' old DMs.

lib/pleroma/conversation.ex

@@ -72,4 +72,18 @@ defmodule Pleroma.Conversation do
       e -> {:error, e}
     end
   end
+
+  @doc """
+  This is only meant to be run by a mix task. It creates conversations/participations for all direct messages in the database.
+  """
+  def bump_for_all_activities() do
+    stream =
+      Pleroma.Web.ActivityPub.ActivityPub.fetch_direct_messages_query()
+      |> Repo.stream()
+
+    Repo.transaction(fn ->
+      stream
+      |> Enum.each(&create_or_bump_for/1)
+    end)
+  end
 end