Improve notebook error logging

[msujew]

What it does

I recently had to debug an issue in a production environment, in which the notebook kernel selection didn't "stick". You could select a kernel, but it wouldn't actually apply. The kernel selection silently threw an error in that case. This change adds a console error in case this happens.

How to test

The changes should be pretty self-evident. However, you can test whether

1. Open a new (untrusted) workspace.
2. Set the security.workspace.trust.startupPrompt preference to never.
3. Open a jupyter notebook and select a kernel. An error should be logged into the console.

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[jonah-iden]

works perfectly for me

[JonasHelming]

@msujew I guess you can merge this