Add a user-facing way to "reset" hub storage

[asmacdo]

Users familiar with the terminal can clean up on their own, but for users not very comfortable with the terminal, it would be friendly to help them out a bit.

(Functionally, we could just delete the user home, and next login would rerun the initialization.)

I asked upstream just in case theres something they suggest https://discourse.jupyter.org/t/could-we-add-a-cleanup-for-users/32169

[satra]

fastest way would be to move the directory and run a cron job to delete folders from the moved to directory

mv <userhome> `to_delete/<userhome>-<uuid> # this is instantaneous
add to delete task `to_delete/<userhome>-<uuid> # this can happen in the background

[yarikoptic]

👍 to @satra - was about to suggest the same. Those users though, never know how upset they are, I would recommend to add a suffix, e.g. to_delete/<userhome>-<uuid>-<random> so if prior deletion is not complete yet, and they want to be forgotten again (unlikely but possible) , their desire could be realized without conflict.