Allow selecting Jupyter Server per Notebook or Interactive Window

[syagev]

Would be useful for notebooks as well the interactive window to support being able to pick a server per notebook/interactive window session (like we allow picking kernels).

Originally posted by @rchiodo in https://github.com/microsoft/vscode-python/issues/3104#issuecomment-655041391

[IanMatthewHuff]

Yeah it's just a limitation of our current implementation, but something that would be good to support. We'll prioritize in triage. Thanks for filing the issue.

[IanMatthewHuff]

This is covered by the new insiders kernel picker work, but as that's just a prototype leaving the bug open until it rolls out.

[DonJayamanne]

This will be fixed with the new kernel picker