Upgrade Stripe SDK to Support 100% Off Coupons

[antonioperez]

Description

Fixes #229

This PR updates the Stripe SDK (2025-02-24.acacia) to enable support for 100% off coupon codes during checkout. Stripe only allows no-cost (free) orders starting from API version 2023-08-16. By default, the checkout will allow promo codes.

Reference: Stripe API Changelog – 2023-08-16

Contributor Checklist

• Update e2e tests: If you changed the /template/app, then make sure to do any neccessary updates to /template/e2e-tests also.
• Update demo app: If you changed the /template/app, then make sure to do any neccessary updates to /opensaas-sh/app_diff also. Check /opensaas-sh/README.md for details.
• Update docs: If needed, update the /opensaas-sh/blog/src/content/docs.