Added the changes requested for MM-8860: Bulk import email intervals (#8498) (#9578)

MM-8860: Bulk import email intervals (#8498)

model/preference.go

@@ -42,6 +42,11 @@ const (
 
 	PREFERENCE_EMAIL_INTERVAL_NO_BATCHING_SECONDS = "30"  // the "immediate" setting is actually 30s
 	PREFERENCE_EMAIL_INTERVAL_BATCHING_SECONDS    = "900" // fifteen minutes is 900 seconds
+	PREFERENCE_EMAIL_INTERVAL_IMMEDIATELY         = "immediately"
+	PREFERENCE_EMAIL_INTERVAL_FIFTEEN             = "fifteen"
+	PREFERENCE_EMAIL_INTERVAL_FIFTEEN_AS_SECONDS  = "900"
+	PREFERENCE_EMAIL_INTERVAL_HOUR                = "hour"
+	PREFERENCE_EMAIL_INTERVAL_HOUR_AS_SECONDS     = "3600"
 )
 
 type Preference struct {