Record Errors from handleEmailEvent webhook

This was a side-quest that came out of my work on https://github.com/get-convex/resend/pull/30 and was suggested by @ianmacartney

It might be a better experience for the user that instead of simply logging warnings to the console when an invalid webhook event is received, we instead enter the value into a table for the user's records.

Arguably though a user could simply hook up Axiom to the project and they would get the same sort of thing as they could just look back through the logs for any warnings.

I am going to leave this here for us to consider for future work.

Start by reviewing the handleEmailEvent webhook work in pull request 30 and the current handling of invalid events. Clarify whether records should be stored in a user-facing table or whether console warnings are sufficient, then define the table, stored data, and completion criteria with maintainers.

Written by the indexing model from the issue text.