Is your feature request related to a problem? Please describe.
The current implementation place the annotation tooltip, to the left or to the right of the annotation area (if it's a rectangle) or place it just in the middle for a line annotation.
With that approach, the tooltip can sometime overlap with the current tooltip, or be shown in some weird places

Describe the solution you'd like
I'd like to check if we can move that tooltip to a proper place.

Describe alternatives you've considered
Possible solutions:

• if a data tooltip is already shown, move the tooltip text inside that tooltip (on the header, on on a different row)
• if no data tooltip is shown, display the tooltip but not stocked with the annotation edge. maybe it's better to have it moving together with the mouse.
• avoid showing a real tooltip, and displaying the text somewhere else on the chart: on the title? just below, above the axis?

Additional context
The vislib chart incorporate that annotation inside the tooltip header:

TSVB just have line annotation with tooltip on the icon (we also allow use to add line annotation without icons)

Kibana Cross Issues
n/a

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`