Ghost: Require a production environment to use a live Stripe account

[daniellockyer]

Issue Summary

Ghost currently allows you to connect to a live Stripe account regardless of the environment it's running in. We've seen instances where an export is taken from a live production site and imported into a development site, and this ends up wiping the webhooks from Stripe + breaking Members.

To Reproduce

1. Download an export from a production Ghost site w/ a live Stripe account connected
2. Import this into a local development site
3. Run Ghost
4. Ensure Ghost doesn't connect to this account/errors out

Ghost running in development should ideally only allow the use of a test Stripe account, so Members is still functional for local testing.

Technical details:

• Ghost Version: 3.39.0
• Node Version: 12.18.0
• Database: MySQL

[allouis]

I think we should only permit creating webhooks under these circumstances too, and relying on the Stripe CLI for webhooks in development!