Maintain automated workflows for benchmarking releases in this repo

[joemcgill]

Feature Description

For the last several major WordPress releases, many members of the WP Performance Team have used forks of @swissspidy's https://github.com/swissspidy/compare-wp-performance repo to run benchmarks to compare performance between releases.

This has been very helpful to observe performance changes during beta/RC stages of releases since we can use consistent methodology for each set of benchmarks. It's also given us a reproducible methodology for reporting performance comparisons in end of release performance posts like this one.

To make it easier for WP Performance team members to run these workflows and collaborate on improvements, we could maintain this tool in this repo rather than as different forks that can get out of sync with each other.

[swissspidy]

I once started GoogleChromeLabs/wpp-research#68 to move it to the wpp-research, but I guess moving it here instead makes sense. Definitely shouldn't need to maintain forks etc. People can just be added as collaborators.