Fix container registry CDN redirection graphs
In !4218 (merged) we surfaced new metrics for the registry CDN feature. We missed something very important in that MR: The underlying metrics are counters and not gauges, so we have to apply a rate, we can't simply plot graphs and calculate percentages over counters, otherwise, we have always increasing values.
I noticed this because I turned on the FF in staging and the lines/percentage for redirects to GCS did not go down to (near) zero.
This MR applies rate
on these metrics. As a drawback, we no longer have nice stat panels for the percentages. These are now displayed as percentage timeseries.
https://dashboards.gitlab.net/dashboard/snapshot/XwiZO5rdyPfeGDYO5DPxMh5abVve2dHz - registry: Storage Detail