Implement job-based metric provider

[jessesuen]

This PR adds a job as a metric provider. Success is measured by exit code. If the job completes with exit code zero, then the metric is successful, otherwise it failed.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@b0a5487). Click here to learn what that means.
The diff coverage is 75.34%.

@@            Coverage Diff            @@
##             master     #186   +/-   ##
=========================================
  Coverage          ?   82.33%           
=========================================
  Files             ?       34           
  Lines             ?     3182           
  Branches          ?        0           
=========================================
  Hits              ?     2620           
  Misses            ?      415           
  Partials          ?      147

Impacted Files	Coverage Δ
service/service.go	58.57% <0%> (ø)
providers/job/job.go	100% <100%> (ø)
utils/analysis/analysis.go	97.67% <100%> (ø)
utils/controller/controller.go	94.2% <100%> (ø)
providers/prometheus/prometheus.go	100% <100%> (ø)
rollout/controller.go	61.42% <16.66%> (ø)
experiments/controller.go	65.04% <16.66%> (ø)
analysis/controller.go	50.64% <25%> (ø)
analysis/analysis.go	80.53% <65%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update b0a5487...e41f56e. Read the comment docs.

[dthomson25]

LGTM with minor requests