Re-introduce technical writers in the reviewers roulette

Once !1110 (merged) is merged, technical writers won't be picked in the reviewers roulette anymore.

In a future iteration, we would like to re-introduce technical writers in the roulette with the following specificites:

1. Technical writers should only be suggested for changes made in the doc/ directory because it contains our general guidelines. It should still be up to engineers to review component-specific docs.
2. The roulette should only suggest a technical writer for the initial review as we don't require maintainer-review for GitLab UI's documentation. This means that if an MR only contains changes to the doc/ directory, the roulette should suggest a technical writer for the initial review and a frontend maintainer for the maintainer review.