[Enhancement] Add Apprise support (#170)

* [WIP] add settings sidebar entry and placeholder page

* [WIP] added placeholder UI and logic for settings form

* Added column and UI for apprise server

* Add some tests

* Added placeholder command runner for apprise

* [WIP] Adding apprise package

* Added apprise command runner

* Hooked up apprise notification module

* Ensured apprise was running in verbose mode

* Updated wording of apprise notification

* Added apprise to README

lib/pinchflat/yt_dlp/yt_dlp_command_runner.ex

@@ -0,0 +1,12 @@
+defmodule Pinchflat.YtDlp.YtDlpCommandRunner do
+  @moduledoc """
+  A behaviour for running CLI commands against a downloader backend (yt-dlp).
+
+  Used so we can implement Mox for testing without actually running the
+  yt-dlp command.
+  """
+
+  @callback run(binary(), keyword(), binary()) :: {:ok, binary()} | {:error, binary(), integer()}
+  @callback run(binary(), keyword(), binary(), keyword()) :: {:ok, binary()} | {:error, binary(), integer()}
+  @callback version() :: {:ok, binary()} | {:error, binary()}
+end