vwa(front): Prevent PVCs from being deleted when there is a corresponding notebook

[orfeas-k]

Context

Right now, VWA checks whether a PVC is mounted to a Pod. If not, then it allows users to delete the PVC. When a user stops a notebook server, then the notebook Pod gets deleted. Thus, VWA will allow a user to delete a PVC that used to be mounted to the notebook. This results in the corresponding notebook not being able to start.

Goal

We want to prevent a user from being able to delete a PVC, even when the corresponding notebook is stopped and there is no Pod currently mounted to it.

UX

The ideal UX would be to check for all PVCs which of them can be deleted and disable the delete buttons for the ones that the user cannot delete, so they cannot click an action that we are able to know beforehand it will fail. However, checking if a PVC can be deleted requires checking for mounted pods, as well as CRs (notebooks, inference services etc) that may use the specific PVC even if there is no pod right now (e.g. a stopped notebook). Currently, checking only for mounted pods and notebook CRs takes around 1-1.5s. Since, this approach, in VWA's index page, would require checking for all PVCs beforehand, we see that this implementation may create a huge delay. We would be able to overcome this delay if we had some caching done in the backend. Since, then, we cannot have the ideal UX effectively, this PR gets as close we can to it. That means that it implements the disable beforehand delete icons approach but we will be checking only for notebook CRs using a PVC. This means, that delete buttons will be disabled for PVCs that are being used by at least one notebook (even a stopped one). At the same time, we will expose the following tooltip over a disabled delete icon

Cannot delete PVC <name> because it is being used by the following notebooks:

- <name 1>
- <name 2>
...

while we will also add a Used by column, that will contain links to the notebooks using each PVC.

Screenshots

Disabled butons for PVCs used by notebooks + Used by column with truncated links to these notebooks

Tooltip for disabled buttons

Popover card tooltip for truncated links

[kimwnasptd]

/lgtm
/approve

[google-oss-prow]

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