Add metrics to monitor Backend/CQLStoreManager ThreadPools

[cdegroc]

Now that PR #2700 has been merged, we can tune the Backend and CQLStoreManager ExecutorServices.
In order to better monitor them, we could generate metrics using Dropwizard's InstrumentedExecutorService/InstrumentedThreadFactory.
Here is a first attempt at adding this: cdegroc@589f560

I would like to gauge interest/feedback before opening a PR.

Thanks!

[li-boxuan]

I think that's a very nice feature to have.

[cdegroc]

Opened PR #2744 👍

[porunov]

This feature was implemented by @cdegroc in #2744 .
Closing this discussion as resolved.