Unify metric name and format in client libraries

[NeoCN]

running both golang and java service, and found out the metric name generated was different, for example, with prometheus:

Java：

# HELP jaeger_reporter_queue  
# TYPE jaeger_reporter_queue gauge
jaeger_reporter_queue 0.0
# HELP jaeger_spans_total  
# TYPE jaeger_spans_total counter
jaeger_spans_total{group="sampling",sampled="y",} 152.0
jaeger_spans_total{group="lifecycle",sampled="started",} 152.0
jaeger_spans_total{group="lifecycle",sampled="finished",} 152.0
# HELP jaeger_reporter_spans_total  
# TYPE jaeger_reporter_spans_total counter
jaeger_reporter_spans_total{state="success",} 63.0

Golang

# HELP jaeger:finished_spans jaeger:finished_spans
# TYPE jaeger:finished_spans counter
jaeger:finished_spans 0
# HELP jaeger:reporter_queue_length jaeger:reporter_queue_length
# TYPE jaeger:reporter_queue_length gauge
jaeger:reporter_queue_length 0
# HELP jaeger:reporter_spans jaeger:reporter_spans
# TYPE jaeger:reporter_spans counter
jaeger:reporter_spans{result="dropped"} 0
jaeger:reporter_spans{result="err"} 0
jaeger:reporter_spans{result="ok"} 0

Unify metric name and format in client libraries can help metric collector and monitor

[yurishkuro]

Thanks for opening this. Yes, I just recently merged a change to the Go client with renamed metrics. The objective is to change all clients to emit similar metrics.

I just booked issues for the other clients.

[jpkrohling]

@NeoCN , how did you get the output listed under the "java service" on your first comment?

[NeoCN]

@jpkrohling impl StatsReporter with Micrometer API, then get metrics output with micrometer-registry-prometheus

[jpkrohling]

Is it your own implementation of the StatsReporter? And, more importantly, would you be interested in contributing this implementation? @objectiser has just mentioned Micrometer to me, so, we might solve two items in one :)

[objectiser]

+1 would be great to get this contributed!

[NeoCN]

@jpkrohling @objectiser yes, my own implementation; I can make a pull request tomorrow, it is too late to go bed now.

[yurishkuro]

Some people have complained (#732 and jaegertracing/jaeger-client-java#335 (comment)) that the colon : is not a great namespace separator.