Disable $0 invoice email for free trial subscriptions

[rishi-raj-jain]

from the ticket

When a user starts a free trial subscription, they receive a "thank you for your subscription" email with an invoice for $0.

Requested behavior:

• Option to disable the automated subscription confirmation email when the invoice amount is $0 (free trial)
• Keep the subscription confirmation email for actual paid subscriptions (after trial ends or when upgrading to a paid plan)

This would improve the user experience by only sending confirmation emails when there's an actual payment transaction.

[pieterbeulque]

There is already a PR for this #9291

[pieterbeulque]

Ah, no, that explicitly keeps the subscription_create email. Anyway, it's all releated. #9291 #9287