Repeatable instrumentation pattern for cortex

[jtlisi]

As discussed in #1512 and on the community call a consistent pattern for instantiating metrics in cortex would be ideal. I have created a design document that outlines the issue here: https://docs.google.com/document/d/100HSvgvaswVR96Bmz2BWIL3d9ds6wqNTVI7_vESgOtE/edit?usp=sharing

[stale]

This issue has been automatically marked as stale because it has not had any activity in the past 30 days. It will be closed in 7 days if no further activity occurs. Thank you for your contributions.