Leading line property - a line that connect the label to ground in 3D view

[allyoucanmap]

Description

It would be interesting to add a leading line options to text style symbolizer that show the relation between the label and a position on the terrain. This does not seem an option provided by the LabelGraphics properties so we need to understand if it's feasibility within mapstore context.

Here a possible implementation found on stackexchange that use a billboard graphic to draw a line

https://gis.stackexchange.com/questions/163733/cesium-js-draw-line-binding-a-label-to-a-position

Acceptance criteria

• [ ] evaluate the feasibility of this new property
• [ ] provide implementation proposal

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