Is your feature request related to a problem? Please describe.
Add ability to add annotation to a chart with a rectangle and tooltip.

Describe the solution you'd like
User should be able to define an coordinates for the rectangle & the text to display for the tooltip. User should also be able to define the style for the annotation (fill, strokeWidth, color, etc.) and default to base styles for undefined styles.

Describe alternatives you've considered
This is one of three annotation-related tasks (see #81).

Additional context
Current feature in Kibana:

Kibana Cross Issues

Checklist

• this request is checked against already exist requests
• every related Kibana issue is listed under Kibana Cross Issues list
• kibana cross issue tag is associated to the issue if any kibana cross issue is present