fix(auth): free trial duplicate reminder emails

Because:

- Free trial reminder emails are sending duplicate emails.

This commit:

- Update call of alreadySentEmail, by free trial logic, to pass in
  required current_period_start instead of current_period_end.

Closes #PAY-3652

Author: StaberindeZA

packages/fxa-auth-server/lib/payments/subscription-reminders.ts

@@ -119,7 +119,8 @@ export class SubscriptionReminders {
         days: endingReminderOptions.freeTrialReminderDays,
       });
     }
-    this.freeTrialEndingReminderEnabled = endingReminderOptions.freeTrialEndRemindersEnabled;
+    this.freeTrialEndingReminderEnabled =
+      endingReminderOptions.freeTrialEndRemindersEnabled;
     this.paymentsNextUrl = endingReminderOptions.paymentsNextUrl;
     this.stripeHelper = stripeHelper;
     this.subscriptionManager = subscriptionManager;
@@ -313,7 +314,7 @@ export class SubscriptionReminders {
     if (
       await this.alreadySentEmail(
         uid,
-        Math.floor(subscription.current_period_end * 1000),
+        Math.floor(subscription.current_period_start * 1000),
         emailParams,
         'freeTrialEndingReminder'
       )