MM-11700 Clean up handling of user display names for notifications (#9343)

* MM-11700 Clean up handling of user display names for notifications

model/preference.go

@@ -21,7 +21,11 @@ const (
 	PREFERENCE_CATEGORY_SIDEBAR_SETTINGS    = "sidebar_settings"
 
 	PREFERENCE_CATEGORY_DISPLAY_SETTINGS = "display_settings"
+	PREFERENCE_NAME_CHANNEL_DISPLAY_MODE = "channel_display_mode"
 	PREFERENCE_NAME_COLLAPSE_SETTING     = "collapse_previews"
+	PREFERENCE_NAME_MESSAGE_DISPLAY      = "message_display"
+	PREFERENCE_NAME_NAME_FORMAT          = "name_format"
+	PREFERENCE_NAME_USE_MILITARY_TIME    = "use_military_time"
 
 	PREFERENCE_CATEGORY_THEME = "theme"
 	// the name for theme props is the team id