Documentation search does not work

[Xenonym]

Description
Documentation search does not work.

How to reproduce

1. Use the search box in the sidebar to search for something (e.g. discovery).
2. Be puzzled as to why the search results are always empty, no matter what you seem to search for.

[dbu]

hm, indeed. i will try to update the sphinx version we use to build the doc, it seems quite outdated