Produce a design for a metrics framework

[andygrove]

Design doc:

https://docs.google.com/document/d/17DCBe_HygkjsoMzC4Znw-t8i1okLGlBkf0kp8DfLBhk/edit?usp=sharing

[andygrove]

I think we can close this now since a metrics framework has now been implemented