Added OPML Endpoint for podcast rss feeds (#512)

* Added OPML Endpoint for podcast rss feeds

* changed opml route and added controller test for opml endpoint

* add copy opml feed button

* add copy opml feed button - correct url

* fix html indenting

* add indentation to opml

Co-authored-by: Kieran <kieran.eglin@gmail.com>

* use convention for unused controller params

Co-authored-by: Kieran <kieran.eglin@gmail.com>

* add test for opml_sources helper function

* change opml endpoint to be more inline with the other routes

---------

Co-authored-by: robs <git@robs.social>
Co-authored-by: Kieran <kieran.eglin@gmail.com>

lib/pinchflat_web/controllers/sources/source_html.ex

@@ -43,6 +43,10 @@ defmodule PinchflatWeb.Sources.SourceHTML do
     url(conn, ~p"/sources/#{source.uuid}/feed") <> ".xml"
   end
 
+  def opml_feed_url(conn) do
+    url(conn, ~p"/sources/opml") <> ".xml"
+  end
+
   def output_path_template_override_placeholders(media_profiles) do
     media_profiles
     |> Enum.map(&{&1.id, &1.output_path_template})