Refactor PromMetrics to use Collect functions

[busma13]

This PR makes the following changes:

• Refactor addMetric into individual functions for counter, gauge, and histogram.
• Add collect() parameter to all add<metric> functions.
• Update types:
  • import prom-client types into types package
  • remove duplicate types from terafoundation and job-components and import from types. This required some refactoring to not use context as a parameter, as the context type differs between terafoundation and job-components.
  • Move info metrics of slice, worker, and master into the setPromMetrics() functions.
  • Update PromClient docs and all relevant tests

[godber]

I would like to merge this but I would like @jsnoble to double check some of the lower level type changes. I think he's seen these recently but I didn't want to merge without an OK from him.