add `truncate_mode` for Dendrogram

Hi!

How are you?

I would like to propose a change for the _dendrogram.py file to be able to use truncate_mode parameter from scipy.

From their documentation, the trucate_mode is an optional parameter which can be used to condense the figure, making it more easy to read when you have a large dataset.

This should be as easy as adding the parameter to the create_dendrogram(), which will in turn pass it to scipy's sch.dendrogram()

Thank you for your time.

從 packages/python/plotly/plotly/figure_factory/_dendrogram.py 開始，重點查看第 25 行附近的 create_dendrogram() 以及第 343 行附近對 scipy sch.dendrogram() 的呼叫。檢查 scipy 關於 truncate_mode 的文件，然後確保接受並傳遞該參數，以便按預期壓縮大型樹狀圖。