Add _total suffix for counters reported to prometheus

[objectiser]

Which problem is this PR solving?

As discussed in the prometheus documentation, "an accumulating count has total as a suffix".

Short description of the changes

If the counter does not have the _total suffix, then it will be added.

This change will also be required to bring the Go tracer inline with the metrics being reported by the Java tracer, which is using the micrometer library that applies a similar transformation on the counter metric names. See jaegertracing/jaeger-client-java#564.

Signed-off-by: Gary Brown gary@brownuk.com

[yurishkuro]

Lgtm but we need to decide about the earlier breaking change before we can upgrade go client.

[codecov]

Codecov Report

Merging #54 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master    #54   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          26     26           
  Lines         719    723    +4     
=====================================
+ Hits          719    723    +4

Impacted Files	Coverage Δ
metrics/prometheus/factory.go	100% <100%> (ø)	⬆️

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