feat: get Stripe keys from environment file

[mitjans]

Types of changes

• [ ] Bug fix (a non-breaking change which fixes an issue)
• [x] New feature (a non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Description

By default, get Stripe keys from .env file. This allows us to set Stripe production keys in environment variables when running the application, while the nuxt.config.ts file will only contain test keys (sk_test and pk_test).

Checklist:

• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I have added tests to cover my changes (if not applicable, please state why)

[fuentesloic]

@mitjans can you update the readme as well please 🙏 thanks a lot! it's a great addition! 🚀

[mitjans]

Done! Let me know if you'd change anything :)