Implement validation for mounted pvc upstream

[saffaalvi]

Users can try to create notebook servers that request mounting a read-write-once (single user) data volume that is already in use. This results in a notebook server that will never fully start

We implemented a feature to validate the user's request for volumes on the new notebook server prior to submission, alerting them to this error. This way users don't get stuck with machines that never start.

The commits related to this feature that need to be integrated into upstream code are:

• Jan 4: feat: Add validation for mounted pvc (StatCan/jupyter-apis@f2614b6)
• Jan 4: fix: show error when element is untouched (StatCan/jupyter-apis@22805a3)

[ca-scribner]

@brendangadd Saffa wont get to this one before she leaves so we should either reassign or banish it to backlog :)