Use dedicated reviewer teams in CODEOWNERS

[qmonnet]

Rather than having multiple people pulled for review for each PR, the docs/ repository could be owned by a GitHub team (to be created).

The advantages would be:

• Avoid pulling all owners each time a PR is created. With automatic PR assignment, just one owner would be picked by the GitHub algorithm, balancing the review load, and keeping notifications low for other reviewers. Of course, if the PR owner feels like more eyes are necessary, it remains possible to manually assign more reviewers.
• Draft Pull Requests don't get auto-assignment, meaning that nobody gets useless review notifications as long as the PR remains in draft state.

(Note: This is what we do for the dataplane repository, for an example.)