Better way to handle kernel restarts

[jtpio]

This is an issue for the following TODO:

debugger/src/index.ts

Line 156 in 67441e7

// TODO: is there a better way to handle restarts?

When we update to target JupyterLab 2.0, we might want to have a look at ConnectionStatus and the connecting status to handle kernel restarts:

https://github.com/jupyterlab/jupyterlab/blob/aa09c52b5e6bd2300dd705a784d4f1eb53b40254/packages/services/src/kernel/kernel.ts#L886

We will also have to update to using a SessionContext instead of a ClientSession.

[jtpio]

Related PR: jupyterlab/jupyterlab#7252