Expose the in_queue time as a histogram

[gouthamve]

trafficstars

This would let users have alerts when there is a spike in the queue times.

[marctc]

@gouthamve I'm not sure if I understand this request. Could you elaborate more?

[grcevski]

I think what this refers to is our Go separation of in_queue vs processing time. We split these timings when we produce the trace spans, but we don't provide a metric equivalent for them. So I think Goutham wants us to create a metric series with this data, so that folks can build effective alerts on this.