Switch to prebuilt client in Admin Training?

> `INSTALL_PREBUILT_CLIENT=1` in front of `run.sh` will use a prebuilt client from npm

Perhaps we can try switching to the prebuilt client in admin training, it'd get some more exposure/testing of the feature which could be quite good, and would let us switch from 8GB VMs back to the 2GB VMs so we can have more trainees supported in each event which benefits everyone. I think the node step is also probably ~80% of our wait time during the installation step so this would be fantastic for us.

xref https://github.com/galaxyproject/galaxy/issues/14948

cc @mira-miracoli @cat-bro @natefoo