OEmbed support for PreviewCard (#2337)

* OEmbed support for PreviewCard

* Improve ProviderDiscovery code failure treatment

* Do not crawl links if there is a content warning, since those
don't display a link card anyway

* Reset db schema

* Fresh migrate

* Fix rubocop style issues
Fix #1681 - return existing access token when applicable instead of creating new

* Fix test

* Extract http client to helper

* Improve oembed controller

app/services/fetch_atom_service.rb

@@ -1,6 +1,8 @@
 # frozen_string_literal: true
 
 class FetchAtomService < BaseService
+  include HttpHelper
+
   def call(url)
     return if url.blank?
 
@@ -45,8 +47,4 @@ class FetchAtomService < BaseService
   def fetch(url)
     http_client.get(url).to_s
   end
-
-  def http_client
-    HTTP.timeout(:per_operation, write: 10, connect: 10, read: 10).follow
-  end
 end