Stripe docs improvements

[coolprobn]

Pull Request

Summary: Doc improvements for Stripe so it is easier for newbies to follow instructions step by step and get the working configurations.

I have also added notes on how to enable webhooks in production which I myself had struggled a bit in the start.

Description: While configuring webhooks in production / live app, I had struggled a bit because instructions were not clear enough on what to do and because I was completely new to Stripe. The purpose of this PR is to help anyone starting out to be able to setup everything correctly without having to search in the Internet.

P.S.: A lot of these contents are copied from Bullet Train docs: https://bullettrain.co/docs/billing/stripe