Add announcements (#12662)

* Add announcements

Fix #11006

* Add reactions to announcements

* Add admin UI for announcements

* Add unit tests

* Fix issues

- Add `with_dismissed` param to announcements API
- Fix end date not being formatted when time range is given
- Fix announcement delete causing reactions to send streaming updates
- Fix announcements container growing too wide and mascot too small
- Fix `all_day` being settable when no time range is given
- Change text "Update" to "Announcement"

* Fix scheduler unpublishing announcements before they are due

* Fix filter params not being passed to announcements filter

app/workers/publish_scheduled_announcement_worker.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+class PublishScheduledAnnouncementWorker
+  include Sidekiq::Worker
+  include Redisable
+
+  def perform(announcement_id)
+    announcement = Announcement.find(announcement_id)
+    announcement.update(published: true)
+
+    payload = InlineRenderer.render(announcement, nil, :announcement)
+    payload = Oj.dump(event: :announcement, payload: payload)
+
+    Account.joins(:user).where('users.current_sign_in_at > ?', User::ACTIVE_DURATION.ago).find_each do |account|
+      redis.publish("timeline:#{account.id}", payload) if redis.exists("subscribed:timeline:#{account.id}")
+    end
+  end
+end