MastoAPI: Add user notes on accounts

Signed-off-by: marcin mikołajczak <git@mkljczk.pl>

priv/repo/migrations/20211121000000_create_user_notes.exs

@@ -0,0 +1,17 @@
+defmodule Pleroma.Repo.Migrations.CreateUserNotes do
+  use Ecto.Migration
+
+  def change do
+    create_if_not_exists table(:user_notes) do
+      add(:source_id, references(:users, type: :uuid, on_delete: :delete_all))
+      add(:target_id, references(:users, type: :uuid, on_delete: :delete_all))
+      add(:comment, :string)
+
+      timestamps()
+    end
+
+    create_if_not_exists(
+      unique_index(:user_notes, [:source_id, :target_id])
+    )
+  end
+end