Script to analyze runner usage across repos (#6902)

A helper utility to help understand what runners are used by which repos
in an organization.

Key features:
- It does the analysis by checking the history of runs on all repos
across the organization
- Output is a yml which slices the data in multiple ways for easier
analysis (e.g. it shows which runners are used by which repos and which
repos use which runners)
- Caches github api results to allow for faster reruns

This tool is intended to be invoked on an ad-hoc basis, not as part of
any automation

Author: ZainRizvi