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/controllers/api/v1/announcements/reactions_controller.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+class Api::V1::Announcements::ReactionsController < Api::BaseController
+  before_action -> { doorkeeper_authorize! :write, :'write:favourites' }
+  before_action :require_user!
+
+  before_action :set_announcement
+  before_action :set_reaction, except: :update
+
+  def update
+    @announcement.announcement_reactions.create!(account: current_account, name: params[:id])
+    render_empty
+  end
+
+  def destroy
+    @reaction.destroy!
+    render_empty
+  end
+
+  private
+
+  def set_reaction
+    @reaction = @announcement.announcement_reactions.where(account: current_account).find_by!(name: params[:id])
+  end
+
+  def set_announcement
+    @announcement = Announcement.published.find(params[:announcement_id])
+  end
+end