Display additional series for a single chart

Resources

FE @jivanvl

Presently within our performance charts, we can only display a single series on a chart. While this was the minimal feature we could deliver to support additional data types, it does mean we miss some opportunities to display information together that is relevant.

A great example is trying to display something like the HTTP responses from an HA Proxy server. It would be great to show the number of HTTP responses that are either 2xx, 4xx, or 5xx on a single chart. This can provide a quick indicator into the overall health of the server, and whether anything strange is occurring. (Like maybe a dead link generating lots of 400s)

We actually have support for this within the data format added in https://gitlab.com/gitlab-org/gitlab-ce/issues/28717. We now just need to ensure:

1. The front end is capable of displaying the additional series within a single chart.
2. The backend is capable of generating the data required for the front end.

As for the look and feel, it should match our original vision for the dashboard:

There are two potential ways for multiple series to occur:

1. There are multiple queries specified for a single chart
2. A single query returns multiple metrics, typically with different label values. For example the http response type could return a series each for 2xx, 3xx, 4xx, and 5xx.

Proposal

Make the Canary series colors the same as for the Stable series: https://gitlab.com/gitlab-org/gitlab-ee/issues/2594#note_37825249