Support multiple metrics for each page
Right now in %10.3 we support only a single metric per page, and so we have standardized on the overall performance score.
We should extend our comparison logic to support additional metrics for a single page, we should consider targeting the following high value ones:
- Total content size
- Total transfer size
- Time to first visual change
- Time to last visual change
- Number of requests
- Script tags
These will require https://gitlab.com/gitlab-org/gitlab-ee/issues/4367 in order to support.
We will also need to do some testing on the variance of the timings, and how repeatable we can get them within a reasonable number of tests. From their documentation it seems like they can vary a good deal: https://www.sitespeed.io/documentation/sitespeed.io/continuous-integration/#travis
For these we may need to consider a "no change" or "yellow" state if the result is within X%, instead of directly marking it as an improvement or degradation.