[MainUI - echarts] Lazy Loading for additional chart types

[jsjames]

I understand that we don't want the javascript bundle to grow excessively and so we don't include all chart types. Has anyone looked at how lazy-loading for additional chart type can be done? I'd like to see the custom chart type added and recently saw a request for sankey.

[florian-h05]

This can probably be done similarly to lazy loading of the locales in #3136.
The webpack bundle report shows that each locale is in its own chunk, and hence will be loaded only if needed.