Fixes #87744 by allowing in AddLayers customization of the url used as l...

...ocal source so we don't necessarily use the layer source defined as local in composer.html as source for layers in the wms wizard. We use this new customization feature so we configure the url to use the public workspace. This public workspace is also configurable, so it could be used to de-gore-ize the js cose if that's finally done.