Incorporate updated antora-lunr search once merged there

Tracking issue for search: @gpx1000 came up with a big improvement which we currently incorporate into our build environment, and someone was kind enough to boost that into an MR in the antora-lunr repo: https://gitlab.com/antora/antora-lunr-extension/-/merge_requests/93 . Once that is merged and published in a package update, we should migrate over to the upstreamed fix and stop using the local one.