Elasticsearch searches through the project description

What does this MR do?

When ES search is enabled we also take into account project description field (which is already indexed)

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

It improved the search experience significantly.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• [ ] Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-org/gitlab-ee/issues/2367