collab: Lay groundwork for reconciling with Stripe using the events API (#15459)

This PR lays the initial groundwork for using the Stripe events API to
reconcile the data in our system with what's in Stripe.

We're using the events API over webhooks so that we don't need to stand
up the associated infrastructure needed to handle webhooks effectively
(namely an asynchronous job queue).

Since we haven't configured the Stripe API keys yet, we won't actually
spawn the reconciliation background task yet, so this is currently a
no-op.

Release Notes:

- N/A