Allow phased rollout of rule changes

[kentquirk]

Is your feature request related to a problem? Please describe.

Sometimes changing refinery rules is risky; it would be nice to be able to reduce the risk by rolling out rule changes to a subset of traces and tagging them with metadata that allows them to be distinguished.

Describe the solution you'd like

• Identify the sets of rule alternatives
• Identify the percentage that should go to each alternative (should add to 100%)
• Use traceID to select which alternative is selected
• Adjust percentages without requiring a refinery restart

Additional context

This idea came up during a customer interview.