[FEATURE REQUEST] OAuth Source Providers

[subomi]

Currently, the flow to ingest webhook events in an incoming project is to

1. Create a Source
2. Retrieve the Source URL.
3. Add Source URL to your Providers webhooks dashboard.

Many of these Providers (e.g. Shopify, GitHub, Stripe) provide OAuth, so we can cut this process down to the user using only the Convoy dashboard to set up webhooks on their provider end-to-end.