KubeSpawner 7 beta review/release effort

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Opened to make some open source work more visible.

This is largely reviewing/testing/releasing of jupyterhub/kubespawner#744. A plan is detailed in jupyterhub/kubespawner#744 (comment).

Remaining work tracked via jupyterhub/kubespawner#850.

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Removing this to be tracked internally in 2i2c. I'm working towards this but tracking it outside of 2i2c though from jupyterhub/zero-to-jupyterhub-k8s#3406 and jupyterhub/kubespawner#850