typename field in advanced metadata form should be read-only or excluded

[fvicent]

The advanced metadata form has a field to edit the typename of a layer:

However, the submitted value always gets reverted by a post_save signal:

https://github.com/GeoNode/geonode/blob/96566be47c75b6932e36bb565b33ae97ddc39d93/geonode/geoserver/helpers.py#L2171

Thus that field is not actually editable. If this is to be expected, it would be reasonable to make the textinput read-only.