Don't show unclickable links in dialogs

[kieferrm]

We usually show "Learn more..." buttons instead.

[IanMatthewHuff]

Validation notes:

This is for a server error with the web extension. You need to be running web, and then you can just try to connect to a junk server name to test it.

The UI varies a bit based on if you are on the kernel picker experiment or not. I've fixed both scenarios.

With jupyter.showOnlyOneTypeOfKernel on, the modal dialog shown above will be replaced with a non-modal error dialog with different wording. With that value false you will get a general server connected error in the validation box, and a non-modal error that gives information specific to the web failure connection case.