[public-api] Add a placeholder Stripe webhook

[andrew-farries]

Description

Add a placeholder Stripe webhook to the public-api component.

In later PRs, the webhook will:

• receive invoice.finalized events from Stripe.
• invoke RPCs on the usage component to update usage records to show that they have been included in a particular invoice.

This PR is a re-do of #11776, which added the webhook to the usage component directly.

After some discussion on that PR and internally, it was decided to move it to the public API and have the pubilc API invoke RPCs on usage instead.

Related Issue(s)

Part of #9036 and #10937

How to test

• Install the stripe CLI into the workspace and run stripe login.
• Port forward to the database in the preview environment:

kubectl port-forward svc/mysql 3306:3306

• Run the public-api-server component locally:

cd components/public-api-server
go run . run  

• Forward stripe events to the local webhook endpoint:

stripe listen --skip-verify --forward-to localhost:9002/webhook

• Trigger a series of Stripe events:

stripe trigger invoice.finalized

This should start a series of Stripe events (setting up a customer and payment methods), each of which should be handled with a 200 OK by the webhook:

Release Notes

NONE

Documentation

Werft options:

• /werft with-preview

[werft-gitpod-dev-com]

started the job as gitpod-build-af-stripe-webhook-on-public-api.2 because the annotations in the pull request description changed
(with .werft/ from main)

[easyCZ]

Love how easy this now is.