Update hardware requirements documentation

[szymontrocha]

The current https://docs.perfsonar.net/install_hardware.html says "The perfsonar-testpoint bundle may work with 2GB of RAM, but 4GB is recommended" and for toolkit "8GB of RAM". This is no longer true with the current Opensearch for toolkit. Unfortunately this is for sure not true for testpoint which is no longer lightweight but clearly pscheduler fills the 8GB memory for most of the day.
We need not only to optimise the sytems (see perfsonar/pscheduler#1502 ) much more but also update hardware recommendations.