closing tabs doesnt dispose voila kernels

[dfguerrerom]

We already have discussed this, but I just want to track the progress on this issue.

If you open sepal_ui or jupyter based applications, when you close the sepal tab, the kernel doesn't get killed and therefore it remains as ghost, consuming memory.

The problem happens because voila only kills the kernel when the app is loaded in a tab and the tab is closed, producing a beforeunload event which sends a beacon: https://github.com/voila-dashboards/voila/blob/9982c78931fd5fbab60b4edc5f00cb353665c9a2/packages/widgets_manager8/src/index.ts#L75, when sepal closes a tab, it doesn't produce that event and therefore the kernel remains running.

Also, in sepal.io, when the app is launched as independent browser tab, the beacon is not sent properly in Mozilla, I have reported the error here jupyter-server/jupyter_server#1466.