Enhancement: User defined variables on HTML dashboard

**Josephine** ([Bug 65822](https://bz.apache.org/bugzilla//show_bug.cgi?id=65822&redirect=false)):
It is currently impossible to plot two or more user defined variables to the HTML custom graph.

I have two user defined variables (two DB search algorithms, whose response times is calculated in a groovy script) and wanted to see a graphical comparison of their performance.

My work around was using a tag in the backend listener and saving the variables into influxDB and visualisation on Grafana.

Would be nice to have everything on the HTML dashboard.
Thanks.

Severity: normal
OS: All