Add breakpoints to notebook for debugging

[frithjof_v]

It would be great if it was possible to create breakpoints inside Fabric notebook cells to make debugging easier.

In the web portal.

[Tom_Fosterbi]

A good way to implement this would be on top of the existing pdb breakpoint() function. Apparently, (although I haven't tested) This works in the fabric vscode extension but it would be good to have it work in the fabric web portal.