This has been possible for ages. The built-in text panel has an HTML option (though you have to disable this setting to allow script tags: https://grafana.com/docs/grafana/latest/installation/configu...)

There are some external plugins that offer more advanced support:

- https://grafana.com/grafana/plugins/aidanmountford-html-pane... - https://grafana.com/grafana/plugins/ryantxu-ajax-panel