Investigate why failed Edge/IE imports weren't logged

[d12]

In https://github.com/education/classroom/issues/2431, there were a number of failed imports but we had no metrics indicate this. In the future, issues like this should surface in our dashboards so we can identify issues earlier, and accurately quantify impact.

cc @spinecone

[spinecone]

I'm not yet certain if this was a case of imports failing or not starting at all. We can add more metrics for API requests that explicitly fail (including browser info), but I'm not sure what would the best way to log imports that never start.

[spinecone]

Talked with @JessRudder today about possible ways to prevent problems like this from coming up again:

• Automated frontend tests for different browsers (i.e. selenium)
• Tracking javascript errors (sentry)
• Baselines for the number of imports we expect to see per day, per browser, with an alert if we go below that number
• In the retrospective today it was discussed how users of classroom use a wider range of browsers than some of us are accustomed to supporting on github.com. Whenever possible, we could simplify the frontend so that more browsers are supported by default, rather than refining complex features to work on specific browsers (this came up recently in the bug with searching on firefox).