Refactor create_profile to use Stripe gem

[brchristian]

This PR is a replacement / extension for the work in #77. It can commit cleanly if #77 is merged, or alternately #77 can be closed and this PR can take its place.

Changes from #77:

• Now includes (passing) tests for maintaining stable Stripe customer profiles across purchases when using V3 Intents! 🎉 In my view, that makes this a complete solution to Reuse Stripe profiles when customer adds a new credit card #26.
• Uses the official Stripe gem rather than ActiveMerchant for the create_profile method, a stepping stone to the long-term goal of Roadmap to remove ActiveMerchant dependency? #74.

I’m very pleased with this result.

@spaghetticode Your code review of #77 was amazing, and I incorporated all of your suggestions there into this PR as well. What do you think?

[stale]

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