[Enhancement] Redownload new media after a delay (#173)

* Added redownload-related columns

* Added methods for fetching re-downloadable media items

* Filled out redownload worker + tests

* Added redownload worker to config.exs cron

* Added to UI and README

priv/repo/migrations/20240409224152_add_redownloaded_fields.exs

@@ -0,0 +1,13 @@
+defmodule Pinchflat.Repo.Migrations.AddRedownloadedFields do
+  use Ecto.Migration
+
+  def change do
+    alter table(:media_profiles) do
+      add :redownload_delay_days, :integer
+    end
+
+    alter table(:media_items) do
+      add :media_redownloaded_at, :utc_datetime
+    end
+  end
+end