Add a Zapier service integration

[rgalanakis]

https://zapier.com/help/create/code-webhooks/send-webhooks-in-zaps

We should require a Whdb-Secret header to validate the webhook.

No denormalized columns, just put it into data.

Migrated from webhookdb-api#435. Opened by @rgalanakis

Opened at: 2022-08-02T05:24:55Z

[rgalanakis]

Need to think through what we want here.
I started building an integration, which I think would be neat to proxy on webhooks from other services, but will need some real use cases. Like, we could forward Google Forms changes to a generic 'blob' integration, where we can't have a service send arbitrary webhooks. We can use some API token authentication there, so we can bypass the 'webhook verification'- then we don't need the customer to set up custom secrets for every webhook they set up, just set up auth once for the integration.
We will probably need some way to pass along the 'external id' of the blob, too, so updates can be done, not just inserts.

Original Comment by @rgalanakis