Track failure responses and present them on the HTTP view

[ppcano]

When the SUT starts throwing errors, you often want to check the response body of the failing requests.

To see the info of the failing requests, the user has to update the script to log the failing requests - requiring manual work and adding some boilerplate code. I think the k6 Cloud could be more helpful in this common case.

When the body of a failing request is present, k6 Cloud could automatically save the error data (limiting to a number of error logs per URL request). This will allow presenting error data in context as k6 Cloud does for other k6 internal errors, helping users figure out the problem quickly.

[markjmeier]

Shared with Lukasz for consideration as part of insights team