Move database page to infra/database and small edits to it

\cc @yorickpeterse , this is from https://gitlab.com/gitlab-com/www-gitlab-com/merge_requests/5373, which became too large and unwieldy. I will merge this now, it includes edits you proposed in the prior MR, feel free to make new edits from here on.

\cc @pcarranza @stanhu