Add text annotation

[emmacunningham]

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

Describe the solution you'd like
User should be able to define an x, y starting coordinate for the text along with a way to customize text style.

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

[markov00]

can the following feature #67 be included in this?
Or at least we can think of internally use text annotation for that case

[wylieconlon]

We are making plans for annotations in Lens, and I think we would want to support text annotations in the long term. My assumption is that text annotations are:

• Interactive with tooltips
• Positioned next to a point on the chart
• Using an arrow/line to mark their origin

Something like the google annotation chart is more powerful than we need, but a good starting point.