Broken link to ppdata-archive

[nikohansen]

The first link provided here https://coco-platform.org/data-archive/ (namely https://coco-platform.org/ppdata-archive) is broken.

We have https://numbbo.github.io/ppdata-archive/ linked from the home page and we have selected comparison data under each suite like https://coco-platform.org/testsuites/bbob/performancecomparisons.html

I am not sure what the "correct" fix is or whether the link is supposed to be created in future.