FIX: refresh flags cache after update (#27909)

`after_commit` should be used before refreshing processes to be sure that the database is already updated.

Also, MessageBus is used instead of events as MessageBus works correctly with many processes;

app/models/flag.rb

@@ -10,8 +10,7 @@ class Flag < ActiveRecord::Base
 
   before_save :set_position
   before_save :set_name_key
-  after_save :reset_flag_settings!
-  after_destroy :reset_flag_settings!
+  after_commit :reset_flag_settings!
 
   default_scope { order(:position).where(score_type: false) }
 
@@ -27,7 +26,7 @@ class Flag < ActiveRecord::Base
   def self.reset_flag_settings!
     # Flags are memoized for better performance. After the update, we need to reload them in all processes.
     PostActionType.reload_types
-    DiscourseEvent.trigger(:reload_post_action_types)
+    MessageBus.publish("/reload_post_action_types", {})
   end
 
   def system?

app/models/post_action_type.rb

@@ -11,8 +11,6 @@ class PostActionType < ActiveRecord::Base
     ApplicationSerializer.expire_cache_fragment!(/\Apost_action_flag_types_/)
   end
 
-  DiscourseEvent.on(:reload_post_action_types) { self.reload_types }
-
   class << self
     attr_reader :flag_settings
 

config/initializers/004-message_bus.rb

@@ -132,3 +132,7 @@ if Rails.env == "test" || $0 =~ /rake$/
   # disable keepalive in testing
   MessageBus.keepalive_interval = -1
 end
+
+if !Rails.env.test?
+  MessageBus.subscribe("/reload_post_action_types") { PostActionType.reload_types }
+end