Allow the dashboard builder to render code cells

[maximlt]

The new Volumetric Imaging example (holoviz-topics/examples#454) added to examples.holoviz.org leverages the feature added in Panel 1.4 that allows serving a notebook that doesn't contain any .servable() call. The notebook is written in a way that implies the code is meant to be read too, however, Panel doesn't render the code cells at all. It'd be nice if there was a way to declare the code cells must also be rendered.

[droumis]

What do you think about a cell tag? I imagine that the more common use case might be wanting to selectively include certain code cells. In the cases that someone wants to include ALL the code cells, it might be annoying but still tolerable..?

[maximlt]

I suggested a toggle that enables displaying all the code cells as the workflow with the builder is roughly (IIUC): Serve notebook (e.g. via the preview) -> Rearrange/delete the Editable template -> Changes are saved as metadata in the notebook. I thought having to set a cell tag didn't fit much in that workflow. Users can manually delete the code cells they don't want to display.

[philippjfr]

While they can delete the code cells, I'm not convinced it's a good experience to include them by default. Don't have a good suggestion for toggling the behavior though.

[maximlt]

Yep I agree they shouldn't be included by default.

[philippjfr]

What would be possible is to toggle the behavior using a URL query parameter (e.g. ?include_code=1 or whatever) and then add a checkbox to the JupyterLab extension that toggles the query parameter on and off.