Trial upgrade z2jh to v4 with jupyterhub v5, kubespawner v7, and oauthenticator v17

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This EPIC tracks trialing upgrading to z2jh 4.0.0.

• JupyterHub 5 upgrade verification
  • Trial upgrade a staging hub and verify that currently running user servers keep running OK
  • Trial using an image with jupyterhub 3 installed
  • Trial using an image with jupyterhub 4 installed
• Kubespawner 7 verification
  • Trial upgrade a staging hub and verify home directories are retained by using subPath: "{escaped_username}" instead of subPath: "{username}"
    Part of Testing upgrade from jupyterhub 3.3.7 to 4.0.0-beta.4 #4979.
• OAuthenticator 17 verification
  • Trial upgrade a staging hub involving github auth
  • Trial upgrade a staging hub involving google auth via cilogon

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This was completed by #4979 where z2jh 4.0.0-beta.4 was tested, and misc issues detected has been fixed upstream already for z2jh 4.0.0 which is now out.