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/models/concerns/account_interactions.rb

@@ -84,6 +84,7 @@ module AccountInteractions
     has_many :muted_by, -> { order('mutes.id desc') }, through: :muted_by_relationships, source: :account
     has_many :conversation_mutes, dependent: :destroy
     has_many :domain_blocks, class_name: 'AccountDomainBlock', dependent: :destroy
+    has_many :announcement_mutes, dependent: :destroy
   end
 
   def follow!(other_account, reblogs: nil, uri: nil)