Missing Endpoint Metrics in Collector

[guanw]

Requirement - what kind of business use case are you trying to solve?

Endpoint metrics are missing. Right now collector can receives spans from TChannel, gRPC and HTTP. We should have a metric that indicates where spans come from in collector.

Problem - what in Jaeger blocks you from solving the requirement?

None

Proposal - what do you suggest to solve the problem or improve the existing situation?

Add the metrics to cmd/collector/app/metrics.go and update interfaces to emit metrics from different endpoints.

Any open questions to address

None