Expose Notebook idleness information in the JWA

[kimwnasptd]

/kind feature

Why you need this feature:
In KF 1.5 and #6297 we extended the notebook controller to expose a idleness information to each Notebook CR.

But this information doesn't get shown to the user in the web app

Describe the solution you'd like:
Add a column in the Jupyter web app that exposes the timestamp of when was the last activity of each Notebook

Anything else you would like to add:
We should use the same component we have for showing dates for this in the frontend

I do have a draft of this and can send a PR

[kimwnasptd]

This has been implemented in #6544