Expose colour and tooltip properties for each segment in the DonutChart component

[danielpacak]

Describe the problem/challenge you have

In starboard-octant-plugin, which is written in Go, we'd like to use the DonutChart component to visualise a vulnerability summary. However, we cannot map predefined colours (red, orange, green) to all severity levels (CRITICAL,HIGH,MEDIUM,LOW,UNKNOWN)

Describe the solution you'd like

Make the DonutChart component more generic so it can represent Pod or Node status, as well as such custom thing such as vulnerability summaries.

Anything else you would like to add:

N/A

Environment:

• Octant version (use octant version): 0.16.0
• Kubernetes version (use kubectl version): any
• OS (macOS 10.15, Windows 10, Ubuntu 19.10 etc): any