Speed up some rake tasks by moving execution to Sidekiq (#7678)

* Speed up some rake tasks by moving execution to Sidekiq

mastodon:media:remove_silenced
mastodon:media:remove_remote
mastodon:media:redownload_avatars
mastodon:feeds:build

* Fix code style issue

app/workers/maintenance/uncache_media_worker.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+class Maintenance::UncacheMediaWorker
+  include Sidekiq::Worker
+
+  sidekiq_options queue: 'pull'
+
+  def perform(media_attachment_id)
+    media = MediaAttachment.find(media_attachment_id)
+
+    return unless media.file.exists?
+
+    media.file.destroy
+    media.save
+  rescue ActiveRecord::RecordNotFound
+    true
+  end
+end