Update Documentation for Admins regarding Puma by Default

We need to update the documentation for Puma-by-default in our administrative documentation in addition to our high availability documentation.

Example: https://gitlab.com/gitlab-org/gitlab/-/blob/593e74a8048952ae3b9cd9db46bbda448d290f87/doc/administration/operations/index.md

See comment: omnibus-gitlab!4141 (comment 333385016)

Opening an issue specifically to track that work and tie it to an epic to keep this work tracked on deliverable boards.

cc @ljlane @mendeni @axil