website: add git repo metadata to result view page

[crazy-max]

Each result has a metadata.txt file which contains repo and commit info like https://github.com/moby/buildkit-bench/blob/gh-pages/result/20240915-010636/metadata.txt

It would be handy to display this information on each result page: https://moby.github.io/buildkit-bench/#/result/20240916-110219

Bonus: we could also find the related PR based on the commit.

[crazy-max]

With #103 we now need to use the gha-event.json payload instead of old metadata.txt.