WIP: Polyfill error ratios as zero for absent error ratio series
Many error series in the GitLab application are lazy: that is, the series does not exist until the error occurs.
This means that after an application restart, we tend to get a lot of "holes" in our error metrics, which slowly fill in as errors occur.
In low RPS environments such as staging, this can take a very long time to happen.
This MR makes a simple change to set the error rate as zero for these components, rather than absent.
With this change, there are at present, about 140 series.
Without this change, we only see about 70 of these series
Edited by Andrew Newdigate