Add user and hub to websub client subscriptions.

lib/pleroma/web/websub/websub_client_subscription.ex

@@ -1,5 +1,6 @@
 defmodule Pleroma.Web.Websub.WebsubClientSubscription do
   use Ecto.Schema
+  alias Pleroma.User
 
   schema "websub_client_subscriptions" do
     field :topic, :string
@@ -7,6 +8,8 @@ defmodule Pleroma.Web.Websub.WebsubClientSubscription do
     field :valid_until, :naive_datetime
     field :state, :string
     field :subscribers, {:array, :string}, default: []
+    field :hub, :string
+    belongs_to :user, User
 
     timestamps()
   end