[Feature Request] Error handling Web Hook / Failure alert

**Problem**

One of our projects supports on-the-fly profile creation - when an Authgear user logs in, if a corresponding profile is not found, we consider it a new user and will create a new profile for the user on the fly.

As we also support account deletion (per Apple's requirement for apps) - we suspect there might be cases where the user tried to delete their account, only that the Authgear user deletion failed, but the app-specific profile's deletion was successful.

Is such case, if the user tries to login again with the same Authgear user (e.g. to verify the account has been deleted), the user might see a new profile be created instead, because it fell into the first login flow.

Our understanding is that, currently Authgear doesn't tell the if an operation has failed.

**Appetite**
> How much time do we want to spend and how does that constrain the solution? (Usually 2 weeks or 6 weeks)

I am not sure if this is something I should fill?

**Solution**

Provide web hooks / error reporting when an operation fails?

**Rabbit holes**

We referred to Paypal's implementation of payment event notification, it took an "exponential backoff" approach, notifying the client server multiple times in the course of 3 days.

**No-goes**

Nil.

No files, tests, or entry points are named in the issue. Start by tracing how account deletion and other operations report failures, then clarify which events, delivery behavior, and completion checks the requested alerting must cover.

Written by the indexing model from the issue text.