Support overlays stacking order

[marcellobarile]

Is your feature request related to a problem? Please describe.

When dealing with custom overlays (e.g. tooltips), overlapping can be a problem and can be solved only with CSS workarounds.

Describe the solution you'd like

It would be comfy to be able to define the order programmatically, or at least be able to set a given overlay to the foreground.

Additional context

The need has been raised while working on: https://github.com/camunda/web-modeler/issues/2744

[marstamm]

Thank you for reporting, it makes sense to have this. I'll move it to the backlog for now