Retire Algolia search

What does this MR do and why?

Removes Algolia code, and updates production to use Google Programmable Search.

Closes #1373 (closed)

Screenshots, screen recordings, or links to review app

Review app: https://gps-rc-1.docs.gitlab-review.app/

Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Configure a local GitLab Docs environment: https://gitlab.com/gitlab-org/gitlab-docs/-/blob/main/doc/setup.md.
2. Check out this branch.
3. Compile the site with Google search and verify you can run searches:

make clean && GOOGLE_SEARCH_KEY="AIzaSyAUCkVNs7JsHYKISjVrVv1PGXg9WQr1MCQ" SEARCH_BACKEND="google" bundle exec nanoc compile
bundle exec nanoc view

4. Compile the site with Lunr search and verify you can run searches:

make clean && make compile
make build-lunr-index
bundle exec nanoc view

Merge request acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this merge request.