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

まず、Dash Tooltips tutorialを期待される動作として使用し、graph_objs.Scatterについて説明されているホバー動作とgraph_objs.Indicatorオブジェクトを比較します。現在の「Invalid property specified」エラーとcallbackの動作を確認し、そのうえで、既存のグラフオブジェクト検証を壊すことなく、Indicatorが要求されたホバーコンテキストをサポートしていることを検証します。