Algolia DocSearch - ranking results

Show GitLab results first, then Omnibus, then Runner.

Ref: https://www.algolia.com/doc/guides/ranking/personalization/?language=instantsearchjs#scoring-with-filters-and-facets

I want to do this for a long time and also @dblessing asked for this some time ago :) I finally figured out how to do it 😅

How to test this:

• Go to http://docsearch-ranking.178.62.207.141.xip.io/ee/README.html and type "inst" (for "install") in the search bar: Algolia will retrieve GitLab Install doc first
• Go to https://docs.gitlab.com/ee/README.html and type "inst" (for "install") in the search bar: Algolia will retrieve Install Runner doc first

Other tests are very welcome!

cc/ @gl-docsteam FYI