Do object insertion through Cachex

So we don't flood our postgres logs with errors. Should also make things
slightly faster.

lib/pleroma/web/activity_pub/utils.ex

@@ -134,14 +134,8 @@ defmodule Pleroma.Web.ActivityPub.Utils do
     context = context || generate_id("contexts")
     changeset = Object.context_mapping(context)
 
-    case Repo.insert(changeset) do
-      {:ok, object} ->
-        object
-
-      # This should be solved by an upsert, but it seems ecto
-      # has problems accessing the constraint inside the jsonb.
-      {:error, _} ->
-        Object.get_cached_by_ap_id(context)
+    with {:ok, object} <- Object.insert_or_get(changeset) do
+      object
     end
   end