Update Prometheus rules to cover both Unicorn and Puma
There are several metrics in https://gitlab.com/gitlab-org/omnibus-gitlab/-/blob/786360e0fdd29da113e9ab2f5d325b620f478335/files/gitlab-cookbooks/monitoring/templates/rules/gitlab.rules that are specific to Unicorn. Now that Puma is an alternative (and becoming default in 13.0), we should update these rules to cover both Puma and Unicorn.