feat: create test dashboard for PRs

[RodrigoVillar]

During PR review, we should ideally be able to get a preview of the reexecution benchmark dashboard to see how the PR will affect the dashboard. This would have prevented #4396 but more importantly, we shouldn't be testing dashboard changes via pushing to master.

[RodrigoVillar]

After some digging, I don't think it's possible to preview the reexecution benchmark dashboard via a link, with GAB noting this here. However, I do think there's a work-around for previewing the dashboard locally.

To my understanding, GAB does the following:

• Checkouts gh-pages branch
• Updates dev/bench/index.html and dev/bench/data.js
• If auto-push is set to true, it pushes to changes to gh-pages

The workaround then for previewing the dashboard on PRs would be as follows:

• For every PR, run GAB with auto-push set to false
• After running the GAB step, add an additional step to upload both dev/bench/index.html and dev/bench/data.js as artifacts.

To verify that the dashboard is working as follows, reviewers would then need to download both index.html and data.js, and would be able to preview the dashboard by opening index.html in their browser (assuming that data.js is in the same directory as index.html.

[RodrigoVillar]

Digging even further, it appears that in addition to just downloading the artifacts, we can also use a tool such as Preview Pages (https://github.com/marketplace/actions/preview-pages#usage) to then produce a GH pages preview of the dashboard. It then appears that we can provide a way to preview the dashboard via the link.

The updated workflow then for previewing dashboard changes in a PR would look as follows:

• Run re-execution benchmark
• Run GAB with auto-push set to false
• After running the GAB step, use the Preview Pages action to generate a temporary dashboard link (this should be printed in the workflow logs)

The re-execution benchmark should be quick; this will result in data points that don't match with the scheduled benchmark runs but we'll be checking that these points are accurate.