Bot nameplates (#7391)

* Store actor type in database

* Add bot nameplate to web UI, add setting to preferences, API, AP
Fix #7365

* Fix code style issues

app/serializers/activitypub/actor_serializer.rb

@@ -37,7 +37,7 @@ class ActivityPub::ActorSerializer < ActiveModel::Serializer
   end
 
   def type
-    'Person'
+    object.bot? ? 'Service' : 'Person'
   end
 
   def following

app/serializers/rest/account_serializer.rb

@@ -3,7 +3,7 @@
 class REST::AccountSerializer < ActiveModel::Serializer
   include RoutingHelper
 
-  attributes :id, :username, :acct, :display_name, :locked, :created_at,
+  attributes :id, :username, :acct, :display_name, :locked, :bot, :created_at,
              :note, :url, :avatar, :avatar_static, :header, :header_static,
              :followers_count, :following_count, :statuses_count