Validate uuid before forwarding them to db engine

Right now using an invalid uuid as a mutation/query parameter (e.g. `xxxx-xxxx-xxxx-xxxx` or `i-do-not-exist`), will raise an `Unexpected error.` that is sent to the client with the original reason `invalid input syntax for type uuid` raised by the DB engine.

This could potentially allow someone to quickly exhaust the Sentry contingent... as an unexpected error is reported to sentry.