Opt-in to Alpha Labels/Metrics

[johnsonj]

The labels and metric names in develop have changed significantly (#136, #138, #144) and may continue to adapt as we iterate on the nozzle.

In order to allow for the fast iteration of the labels/metrics while releasing reliability improvements we should add a toggle to enable this new behavior. The toggle should be either: master branch as it in v1.0.5 or anything goes alpha behavior. This will help us transition to a 2.0 release where we can break users dashboards.

I believe we can accomplish this relatively easily:

• Restore the original labelMaker as legacyLabelMaker
• Add a flag to config to EnableAlphaMetrics. Plumb through job spec/tile UI.
• Inject the correct labelMaker during App construction
• Add a conditional to the metric prefix assignment (or perhaps refactor this into a service object)

We will drop the opt-in and legacy code paths with the v2.0.0 release.

/cc @fluffle @knyar

[johnsonj]

I don't think this issue is still relevant. Churn has stabilized a bit. The next release will be a massive breaking change but that is warranted. If we start introducing lots of churn after v2.0 then this issue should be revisited.