Refactoring metrics helpers in the workflow

[seanbollin]

What was changed

Why?

A lot of redundant and verbose code for emitting metrics

Checklist

1. Closes

2. How was this tested:

3. Any docs updates needed?

[02strich]

The private type names could be a bit more explicit to metrics, but otherwise looks like a nice improvement.

[seanbollin]

I think I'll add a unit test to this that lists all metrics and what labels they should have

[jaypipes]

@seanbollin That kind of a unit test generally just provides friction when evolving the set of metrics, in my experience. Better to skip that kind of a unit test (that really is just going to be a repeat of the const/var definitions in wci/metrics/metrics_defs.go) and instead focus on tests that verify the value of a particular metric has been updated in an expected way during a single execution of some unit of work -- for example, that a particular counter is incremented or that a duration is within an acceptable range.