setOpacity and opacity options for Marker

[HarelM]

User Story

As a user I would like to be able to set the opacity of a marker when terrain 3D is on in case I override it with css or for whatever other reason

Rationale

When terrain is on and the marker is behind terrain the opacity is set to 0.2 and returned to 1.0 when not behind terrain.
If I set this value in the css I'll get a behavior that is not intended, and therefore there's a need to disable it or define other values beside 0.2 and 1.

Impact

The is a workaround as one can programmatically change this so this is a "nice to have" API for the marker.

[sbachinin]

This has to be closed I guess

[HarelM]

Fixed by #3620