Suggestion: Show benchmark stats relative to some baseline in PRs

[nickchomey]

Its great to see that benchmarks are being run on PRs. But the stats are not shown relative to anything, so theyre only informative if you happen to know previous benchmark values.

It would be great if it could have a column that shows a % or x multiple relative to something like the tip of the main (or other relevant) branch.

It would also be helpful to see some charts of each stat's progress/history, so we can see how it all has improved over time.

[nickchomey]

looks like there's already some mechanism that sometimes does some version of this

eg #6873

as compared to #6881 (comment)