fix: unhandledRejection types are looser than assumed

[pauldambra]

We had a period of c 90 minutes where blob ingestion was failing to start

See https://posthog.slack.com/archives/C0185UNBSJZ/p1698707508193559?thread_ts=1698684867.238139&cid=C0185UNBSJZ

The errors that were (maybe) causing this were hidden because a top level handler for unhandledRejection assumed that it always received an Error from which it could read stack

Slightly ridiculously the error being received was undefined https://posthog.sentry.io/issues/4410219272/?query=is%3Aunresolved+PLUGIN_SERVER_MODE%3Arecordings-blob-ingestion&referrer=issue-stream&statsPeriod=1h&stream_index=2

Looking at https://nodejs.org/docs/latest-v18.x/api/process.html#event-unhandledrejection the signature for the handler is

Event: 'unhandledRejection'
reason <Error> | <any> The object with which the promise was rejected (typically an Error object).
promise <Promise> The rejected promise.

This changes the handler to log the error without trying to read its properties, bringing the log message to almost match the example from the docs