Algolia index - hidden h1s

The problem

With https://github.com/algolia/docsearch-configs/pull/331, we've set only_content_level: true to try to get some hit text when the hit == h1 only. https://gitlab.com/gitlab-com/gitlab-docs/issues/134

We ended up hiding the h1-only results. E.g.: in docs.gitlab.com/search/, search for "gitlab pages", there are no hits in the first page of results.

The solution

I requested to rollback these changes (https://github.com/algolia/docsearch-configs/pull/347), but @s-pace recommends that we change the index structure to https://github.com/algolia/docsearch-configs/blob/1a69251a839ae72d496cdb73e868d14a0fcced62/configs/gitlab_2.json instead :)

To do so, we need some adjustments on our side. MR: https://gitlab.com/gitlab-com/gitlab-docs/merge_requests/219