Add support for workers using scheduled events.

[tomprince]

In particular, ones that don't have a fetch event, but also ones that do.

[evanderkoogh]

Hey @tomprince, I don't actually have permission anymore to make changes to this repo after I left Cloudflare, but with the recent release of AsyncLocalStorage, it is now possible to create an Open Telemetry compatible library that will be easier to work with than this one.

I have been working on it here: https://github.com/evanderkoogh/otel-cf-workers

It is still alpha, but I am expecting it to go into beta/stable over the next few weeks. Support for the scheduled trigger is certainly planned for release there.