Features to pause cell-wise reactivity and long startup time

[yl4070]

Hi, I'd to know how everyone is addressing the heavy computation that may be involved in the notebook.

Since in PlutoUI document, a use case of a button as reactivity as trigger is mentioned, I think it's natural to have the opposite, i.e. pause the reactivity for a specific cell. Such as ones would take a long time to run. This feature resembles isolation function in R's Shiny package. This would also resolve the issue that a computational notebook would take a very long time to startup. The heavy computation can thus become optional or postponed.

Currently, this can be done with a workaround with a condition check. But I think a formal support of pausing reactivity can be useful, which can be a middle ground between Pluto and Jupyter.

Additionally, I think an option to automatically disable all cells at the startup, until being executed manually can also be quite useful, so the users don't need to stare at the notebooks before they can do anything.

This is related to Switch between "Pluto" reactive mode and "Jupyter" mode, but I think the goal is different enough to be a different discussion.