fix handbook and user access inconsistency

Here's what handbook states:

Production access (specifically: ssh access to production) is granted to production engineers, security engineers, and (production) on-call heroes. Staging access is treated at the same level as production access because it contains production data.

Here's what we have in our access roles: https://gitlab.com/gitlab-cookbooks/gitlab_users#currently-defined-roles -- we have the following roles that contradict the handbook: database, monitoring, elasticsearch. The requirement of having the separate staging also doesn't fit into handbook.

@gl-infra @bjk-gitlab Thoughts/feedback? Should we change one or another?