[AWS][Security Hub] Update donut charts with pie/treemap

[kush-elastic]

Description

In general pie/donut charts are not recommended for visualizing any data. Other options would be to use treemap instead where it's much easier to notice the real proportions of data. Or even instead of donut, pie chart can be used because there's more space for labels.

Donut chart panels:

1. Distribution of Events by Region
2. Distribution of Events by Account

Treemap visualization

Pie visualization

Screenshot of dashboard