[Feature request] adding Subplot titles

Hi,

Is there any function like the python version:
fig = tools.make_subplots(rows=2, cols=2, subplot_titles=('Plot 1', 'Plot 2','Plot 3', 'Plot 4'))
https://plot.ly/python/subplots/#simple-subplot

I spent hours today trying to figure that out, the only workaround I found is here:
https://stackoverflow.com/questions/37285729/how-to-give-subtitles-for-subplot-in-plot-ly-using-r
But it might get into trouble when your dataset is dynamic and shareX = T, which you don't know what subplot goes to which location.

首先，将所请求的 R subplot-title 行为与链接的 Python tools.make_subplots 示例，以及针对 shareX = T 的动态数据集所描述的变通方案进行比较。完成的标准是：subplot 标题能够可靠地映射到其 subplot 位置，包括数据集为动态的情况，并且 R API 对外提供此行为。