OCC-333: Fix dependency resolution errors in SubscriptionStripeWebhookEventHandler

[sarahelsaig]

OCC-333
Fixes #548

[sarahelsaig]

How to test:

1. Enable Stripe feature
2. To to Admin > Configuration > Commerce > Stripe API.
3. Fill out your API keys
4. In another tab go to https://dashboard.stripe.com/webhooks/create?endpoint_location=local
5. Follow the instructions, except use --forward-to https://localhost:5001/stripe-webhook to match the hook URL in OCC.
6. You will see multiple [200] POST success messages in the command line.

Note

Using the Stripe CLI to trigger a payment success event may return one 500 response at the end after the successes, because of missing payment intent. That's fine.