Milesight with Chirpstack on GCP


I am trying to connect multiple Milesight gateways (UG65 with firmware to GCP, following and adapting the Guide published in the Chirpstack website (Quickstart Google Cloud Platform).
From the two options I have to connect the Milesight gateway, Semtech works if I install and configure a CGB on a VM in GCP. This case is not useful as I would need to add one CGB for each Milesight gateway that I need to connect (there are several hundreds).
The other option is to use the Chirpstack-generic forwarder, which requires the NS address, the MQTT port, and user credentials and/or TLS authentication.
I wasn’t able to make it work using the Chirpstack-generic.
Looking for any possible help, my questions are:

  1. How is the NS configuration changed when using the Chirpstack-generic forwarder on the Milesight gateway?
  2. As the IoT Core device requires an RS256 key, how and where can I add the file “private-key.pem” ?

I appreciate very much any help on this beginner issues.