Mention deploy node in hup Puma/Unicorn step of multi-node Geo upgrade docs

What does this MR do?

Add explicit mentions of the deploy node in the last substep of Steps 2 and 3 in https://docs.gitlab.com/omnibus/update/README.html#multi-node--ha-deployment-with-geo-premium-only. The previous substep titles explicitly mention if the deploy node is included or not, so this makes the titles more consistent.

This addition is based on feedback from a Geo multi-node upgrade demo

Related issues

Closes #5460 (closed)