Revert "Remove migration"

This reverts commit da0b9403e4.

priv/ingest_repo/migrations/20241112082348_add_channel_to_imported_source.exs

@@ -0,0 +1,9 @@
+defmodule Plausible.IngestRepo.Migrations.AddChannelToImportedSource do
+  use Ecto.Migration
+
+  def change do
+    alter table(:imported_sources) do
+      add :channel, :"LowCardinality(String)"
+    end
+  end
+end