add assert checks at the end of Datalab tutorials to ensure no unexpected issue types were detected

[jwmueller]

When we add new issue type to the default set Datalab detects, we want to ensure it is not detected in any of our old tutorials (at least we want to be aware if it is, so we can comment on it).

Proposal: add an assert at the bottom of each Datalab tutorial that checks basically:

This tutorial only detected the following set of issues: [type1, type2, ...] (which are the issue types we expect the tutorial to detect with > 0 issues in the tutorial dataset)