Add support for passing advanced configuration when using the live data macro

Would be nice to be able to support passing the live data configuration JSON as content of the live data macro.

{{liveData}}
{
  query: {...},
  data: {...},
  meta: {...}
}
{{/liveData}}

This would bring two important benefits:

• support for in-line data source
• ability to perform advanced configuration that is otherwise hard / impossible to do with the macro parameters

The idea is that for the most common use cases it should be enough to use the macro parameters, while for advanced / complex / niche use cases you can pass the live data configuration JSON as macro content. This is needed for instance in order to be able to replace some of the existing live tables where the configuration is not generic enough to be included in the data source, so it needs to be explicit / specified in the live data macro call.

When both macro parameters and macro content is used then we can merge the configuration, giving priority to the macro parameters.