Offchain worker: Enable http2 and improve logging (#10305)

* Offchain worker: Enable http2 and improve logging

Apparently some webpages now return http2 by default and that silently breaks the offchain http
extension. The solution to this is to enable the `http2` feature of hyper. Besides that, this pr
improves the logging to make it easier to debug such errors.

* FMT

* Adds http2 test