Improve sunburst chart for Anomaly Distribution

[yizheliu-amazon]

Given only 1 detector exists, the inside Index circle will have issue in following scenarios:

1. if Linked Label is configured for identifying index, label of Index circle will be invisible;
2. if Fill Label is configured for identifying index, label of it will be overlapped with outer Detector circle

Screenshot of 1st scenario:

Screenshot of 2nd scenario:

We think currently it is fine because sunburst chart does not make big difference if there is only 1 detector + 1 index. We will keep digging into this, and may open issue for elastic-chart to see if we are using it in a correct way or it is bug of the library.

[yizheliu-amazon]

we are also seeing the same issue: elastic/elastic-charts#633

[yizheliu-amazon]

Opened issue to owner of elastic-charts: elastic/elastic-charts#637

[ylwu-amzn]

Test on 7.7, one detector looks like this

[yizheliu-amazon]

Closed by this PR: #260