PLT-7177: Change the default email frequency to 15 minutes if batching is enabled on the server. (#7036)

* PLT-7177: Found default preference that needs to be changed

* PLT-7177: Front end behaves as desired

* PLT-7177: Changed default batching interval on server side

* PLT-7177: Added unit tests for new default interval

* PLT-7177: Removed unused import

* PLT-7177: Renamed constants to increase clarity

model/preference.go

@@ -33,7 +33,9 @@ const (
 
 	PREFERENCE_CATEGORY_NOTIFICATIONS = "notifications"
 	PREFERENCE_NAME_EMAIL_INTERVAL    = "email_interval"
-	PREFERENCE_DEFAULT_EMAIL_INTERVAL = "30" // default to match the interval of the "immediate" setting (ie 30 seconds)
+
+	PREFERENCE_EMAIL_INTERVAL_NO_BATCHING_SECONDS = "30"  // the "immediate" setting is actually 30s
+	PREFERENCE_EMAIL_INTERVAL_BATCHING_SECONDS    = "900" // fifteen minutes is 900 seconds
 )
 
 type Preference struct {