[Feature proposal] Add toleration "hub.jupyter.org/dedicated=user:NoSchedule" to build pods

[jhamman]

I'd like to propose adding a default toleration to binderhub build pods. In most cases, build pods are intended to be scheduled on the same nodes as user notebook sessions so I think the easiest path forward would be to match the jupyterhub taint/toleration for users:

hub.jupyter.org/dedicated=user:NoSchedule

My motivation is that I'd like to restrict scheduling on my user node-pool to only build and notebook pods.

Adding a toleration does not require a matching taint be set, rather it allows the cluster manager to set taints that certain pods can tolerate. For this reason, I don't immediately see any downside to this feature being added. That said, I'm still learning in this space so I'm open to redirection.