Update dependencies for notebook datasource

[mure]

Grafana 8 has been released for a while now, so I updated all the dependencies in the notebook plugin in preparation for some upcoming development. This led to a few build failures and misc. headaches. A summary of the changes:

• Linting fixes
• Type assertions for HTTP errors (this is a band-aid, see TODO comment)
• Styling problems with query builder (side note: I finally figured out how to suppress the zillions of warnings the smart webcomponents CSS was causing during compilation! I added a "browserslist" property to the package.json and explicitly put 'not IE')
• Removing the custom webpack config because the Grafana team fixed the issue I filed 🎉

[mure]

The build was failing on the test monitor data source, so I also updated its dependencies in this PR. This included linting fixes and a better info display for the user on how to use it.