Frontend: auto-select only benchmarks

[ElectreAAS]

For example, at the moment for ppxlib:
Clicking on ppxlib in the sidebar leads to https://autumn.ocamllabs.io/ocaml-ppx/ppxlib which immediately redirects to https://autumn.ocamllabs.io/ocaml-ppx/ppxlib?worker=autumn&image=ocaml%2Fopam%3Adebian-ocaml-5.0 (so we add the worker and the image), but it still says "No data for selected interval".
We could instead link/redirect to https://autumn.ocamllabs.io/ocaml-ppx/ppxlib/benchmark/benchmarks?worker=autumn&image=ocaml%2Fopam%3Adebian-ocaml-5.0 (which links to the "benchmarks" benchmarks (it's their name), on top of the other parameters), which actually produces the graphs.

When there is only one such benchmark we could do that automatically, and when there are multiple, we probably should have something more informative than "No data for selected interval" and instead point to the benchmarks on the left.