Enhanced output for performance testing rig

[rzats]

Prerequisites:

• Unless it is a documentation hotfix it should be merged against the dev branch
• Branch is up-to-date with the branch to be merged with, i.e. dev
• Build is successful
• Code is cleaned up and formatted

Summary

Updates the performance testing rig to make its PR comment output a summary of the run, which looks like this:

[rzats]

Unsure if this will trigger the newer or older version of the GitHub Action, but:

/run performance test

E: nope, looks like the older version for now

[github-actions]

✅ Performance tests complete! Click here to view results: https://github.com/cmu-delphi/delphi-epidata/actions/runs/4286183094

[krivard]

👍 Can merge as-is; question identifies a possible opportunity to reduce some coupling

[rzats]

@krivard requesting a re-review since I applied the change that reduced some repetitive code

[krivard]

👍 Solid!