jbranchaud/egg 270 create lifetime membership checkout session

[jbranchaud]

This PR does two core things:

First, it sets up the pre-purchase flow for Lifetime Subscriptions via the /forever path. This collects an email if the user is not already signed in and then hands them off to a Stripe checkout session.

Second, it handles the post-purchase flow. This sets up egghead-next to process Stripe webhook events for checkout.session.completed via inngest. It will only process for a specific purchase (stripe price ID) because everything else should be handled by the egghead-rails backend.

Note: this depends on some API changes being merged into egghead-rails before this changes can be deployed.

Deployment Task

• [ ] Add checkout.session.completed to the list of events for the production webhook endpoint

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• feat: change stripe sub checkout to named export
• feat: add Lifetime Membership pre-purchase flow
• feat: set up stripe webhooks for inngest
• feat: process stripe webhook with inngest