Support for Dendrogram Diagram

### What problem does this feature solve?
A dendrogram is a diagram that shows the hierarchical relationship between objects. It is most commonly created as an output from hierarchical clustering. The main use of a dendrogram is to work out the best way to allocate objects to clusters.

In our organization we have many use cases where we need to cluster objects/data into hierarchical diagram. Which I am not able find a way to achieve using existing charts in ECharts.

Please let us know in case we can create/extend Dendrograms by customizing ECharts.

### What does the proposed API look like?
A special chart type for 'dendrograms'
type: 'dendrogram',