Allow user to pick from local jupyter session

[DonJayamanne]

When connecting to an existing jupyter session, user needs to enter the URL of the jupyter server. We could instead pre-populate a list with the active jupyter servers.

We already have code to get the list of servers (it includes the token information as well).

[rchiodo]

Is this a must fix?

[ivirshup]

I'd really like this. It's kind of a pain to find the token for a server if that's needed, but vscode should have the rights to figure out tokens on it's own (from jupyter notebook list --json).

[DonJayamanne]

Closing as users can already add jupyter servers manually