Replace fa-search-* icons with GitLab SVG ? icons

As part of the effort to replace FontAwesome icons with GitLab SVGs we need to use the search-plus and search-minus icons instead of the Font Awesome variants.

• 1 times: fa-search-plus
• 1 times: fa-search-minus

When you are done

1. Add screenshots from before + after to make review easier and faster
2. Get UX Review
3. Get Frontend Maintainer review directly

References

• See https://leipert-projects.gitlab.io/is-gitlab-pretty-yet/icons/ for all Font Awesome icon instances
• See http://gitlab-org.gitlab.io/gitlab-svgs/ for all GitLab icons