add hover implementation to graph_objs.Indicator

Following the hovering tutorial for Dash Tooltips, I noticed that the described hovering functionality present in graph_objs.Scatter is not present in graph_objs.Indicator (I get Invalid property specified errors for hoverinfo, and the callback does not fire)

I respectfully request this functionality be extended to the Indicator and thank you in advance for your consideration.

For context behind my request, I am building a dashboard for my workplace that will be used internally and will auto-configure based on the job that is running. The user being able to hover over the graph and view extra context as to what it is displaying would be highly beneficial.

Jules

首先，将 graph_objs.Scatter 所描述的悬停行为与 graph_objs.Indicator 对象进行比较，并以 Dash Tooltips tutorial 作为预期行为。确认当前的“Invalid property specified”错误和回调行为，然后验证 Indicator 支持所请求的悬停上下文，且不会破坏现有的图形对象验证。