Merge request widget "could not retrieve pipeline status" error should be operationally observable

Sometimes the merge request widget will return a response like this:

Could not retrieve pipeline status. For troubleshooting steps, read the documentation.

When this happens, it seems that although this is a user-impacting error, it is not visible from an operational perspective:

1. All HTTP calls association with the polling request returned successful HTTP error codes
2. As far as I know, no log messages or sentry exceptions are logged when this error is generated

Since this has an impact on user-experience, we should, as operators of GitLab.com be able to determine when this is happening and (if possible) why.

At present I don't think this is possible.

Slack thread: https://gitlab.slack.com/archives/C101F3796/p1586860799050700 (while it lasts)

Another Slack thread: https://gitlab.slack.com/archives/C0SFP840G/p1590158858098700