Stop hardcoding reflectors to monitor component: singleuser-server label

[consideRatio]

We have hardcoded kubespawner to monitor pods with the label component: singleuser-server. It would be good if we instead allowed what we search for to be configurable. I know this has been relevant for a minority of z2jh users who wanted to deploy multiple hubs in the same k8s namespace for example, but I'd also like it so that we can update the old label scheme component to the modern app.kubernetes.io/component label.

I think we should introduce a configuration to represent what pods we monitor and manage based on label selection.

Related

• KubeSpawner.component_label configuration
• k8s matchLabels, for Deployment resources for example, declaring how they via labels identify the resources they are controlling