Move user home directories from NFS storage to block-storage backed PVC

[Adam-D-Lewis]

Context

We've had some concerns around IOPS when creating conda environments and writing many small files to disk. Also, potentially, one user can break the home directory of all users currently. We are exploring this in conjunction with a redesign of CondaStore, which stores user environments on their home directory rather than on an NFS drive.

Value and/or benefit

Better isolation
Better Performance

Anything else?

I've explored this further in a branch - #3192

[Adam-D-Lewis]

Other changes will also be required with JHub apps and Jupyter Scheduler: #3192 (comment)