Feedback on experimental tokio runtime metrics support

[gagbo]

Hello,

Recently I had the need to get the metrics of Tokio runtime to be exposed to Prometheus. As the metrics are very unstable for now (It's hidden behind a rustflag), instead of trying to get the metrics here I made an extra library to be more nimble to follow possible breaking changes.

https://github.com/gagbo/rust-prometheus-tokio

It is loosely based on the process collector that already exists here, and I welcome any feedback on it (adding or removing metrics, renaming them, performance implications), as eventually when RuntimeMetrics get stabilized I would like to have this library upstreamed here.

Have a good day,
Gerry