No metrics tag for sampler.type

[guanw]

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

Within Uber we are trying to remove downsampling in collector completely. To do this, we need some insight into samplers used by different services. The current metrics doesn't provide such thing.

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 a new tag in metrics.go named samplerType

Any open questions to address

None