NOTE: Users who have read/write are able to perform this tool.
Format the intended KMZ/L to have one folder, with objects underneath (no sub-folders).
To import a KMZ into the GIS Portal, click the leaf icon "Add Layer"
A modal will follow. Click the drop down under "Select a Layer" to "Upload"
Click "Choose File"
Select the KMZ/KML file and Click Open
After naming the layer, click Create
The data in the KMZ will upload to the layer, retaining its attributes.