ETABS_Toolkit: Add adapter support for Structure.Elements.Opening

[IsakLarbornBH]

Description:

Currently, the ETABS adapter does not support pushing objects of type Structure.Elements.Opening.

Pushing openings as separate objects, rather than as internal panel elements, can be useful in cases where openings cross over multiple panels (as can happen when a panel is split for loading) and need to be treated separately in the model laundry.

My current workaround is to push Openings as Panels with a special section property for identification, then assign them as openings within ETABS. However, being able to push Openings directly would simplify this workflow.