Make hubs compatible with Z2JH 1.0.0

[consideRatio]

Background

Z2JH 1.0.0 introduce breaking changes, we must make some adjustments.

Expected timeline

End of May.

Steps to complete this goal

• Verify outcomes of schema validation using instructions here.
  • Verified outcomes of using basehub and its default values (-> relocate singleuser.admin / cloudResources)
  • Verified outcomes of using daskhub and its default values (-> relocate singleuser.admin / cloudResources)
  • Manually verified the cluster specific deployment configuration (-> relocate homepage)
• Verify we work against k8s 1.17+ clusters
• Verify we use a helm client versioned 3.5+
• Acknowledge that deleting users will now also delete the users associated PVC
• Acknowledge that pods in the JupyterHub helm chart no longer have predefined resource requests (cpu/memory). See Don't set default resource requests jupyterhub/zero-to-jupyterhub-k8s#2034.
• Relocate cloudResources to custom.cloudResources (?) where Z2JH 1.0.0 won't complain about a passed value it doesn't recognize.
• Relocate singleuser.admin to custom.singleuserAdmin (?) where Z2JH 1.0.0 won't complain about a passed value it doesn't recognize.
• Relocate homepage to custom.homepage or perhaps global.2i2c.homepage where Z2JH 1.0.0 won't complain about a passed value it doesn't recognize. Note that global variables are not made accessible from get_config though, but such feature would be acceptable to implement i think.

[yuvipanda]

As usual, a very thorough and thought out issue, @consideRatio. THANK YOU.

I've verified that all our current clusters are on at least 1.19. Opened #412 to decide ongoing policy.

Our GitHub actions use https://github.com/Azure/setup-helm, which uses latest stable version of helm. So that's 3.5.

I opened #415 for custom.cloudResources. I've some more thinking to do for singleuser.admin.

We use a single pre-configured PVC (https://github.com/2i2c-org/pilot-hubs/blob/master/hub-templates/basehub/templates/nfs-pvc.yaml) for all users, and don't use dynamic provisioning at all. So deleting of PVCs doesn't affect us. https://pilot-hubs.2i2c.org/en/latest/topic/storage-layer.html has more info about our home directory storage.

[consideRatio]

@yuvipanda I scanned the cluster specific configs and found jupyterhub.homepage was referenced as well - that will also cause issues.

[yuvipanda]

#417 just moved home page stuff under custom, I think that's good enough for now.

[yuvipanda]

I've some more thinking to do for singleuser.admin.

We should just move it under custom for now I think