Disable user conda and pip installations

[antonvorobets]

I tried doing this by following this suggested implementation:

Failsafe container?

So all that would be needed is to add this to profileList? - display_name: "Failsafe environment" description: "Use this if you get internal error on startup" kubespawner_override: image: jupyter/minimal-notebook:2343e33dec46 enviroment: PYTHONNOUSERSITE: "1"

But then the server fails to start for some reason.

I think many people would appreciate it if this feature could be added as a config parameter