Docs feedback: add how-to/example of how to use multi-series bar charts

[This page](https://grafana.com/docs/grafana/latest/panels-visualizations/visualizations/bar-chart/) would definitely benefit from covering a how-to or an example of how to use multi-series bar charts. The example images include multi-series screenshots. At present, the page seems to document a reference list of what the configuration parameters for the visualization are, but doesn't provide needed examples of how to use the visualization in some context. This YouTube video has > 20k views covering this topic and begins by noticing how the docs are lacking in this aspect: https://www.youtube.com/watch?v=ky78RZ2f7oc These community postings are asking essentially this question: https://community.grafana.com/t/how-to-create-grafana-multiple-bar-chart/87254 https://community.grafana.com/t/multiple-series-from-multiple-variables/6577