Add option to choose N1 vs N2 for custom machine types

[wuservices]

N2 custom machine types allow different configurations vs N1. For some workloads, being able to choose N2 vs N1 for custom machine types will allow for better flexibility and cost savings.

https://cloud.google.com/compute/docs/instances/creating-instance-with-custom-machine-type#n2_custom_machine_types

[supersteves]

They've released E2 machines which are cheaper but don't have sustained discounts, and thus more suitable for a build farm that bursts up and down. You need to be able to choose the machine type, but you can only choose the CPU/memory for an N1 type.

[supersteves]

I know you can use instance templates, but it's not as convenient to set up.

[fatmcgav]

This is technically possible already; however the UI Machine Type selector displays the description rather than the name.

I've addressed that in #42