WebReactiveOptions support for connection metrics

[mnbattaglia]

In the same way that maxIdleTime and maxLifeTime were added in WebReactiveOptions in #559, it would be great to also have the metrics attribute so we can enable/disable this directly from the options.

This was asked in the other issue but maybe it went unnoticed as it wasn't asked in the original title or message. I think it would be really useful and easy to implement.

Thanks!