Update XML for demo PDG portal to match newer format of the production portal

[julietcohen]

Integrate the changes made to the production PDG portal into the demo portal XML. Many of these were inpired or integrated by the Google Fellows in 2024. The changes include:

• integrate layer categories
• set light theme
• default base layer to be Open Street Maps base rather than Bing Satellite Imagery
• default to open to Viewfinder rather than Layers

After this is done, check all that the layers with "visible": false, are not visible by default when you navigate to the demo portal. It seems that this option is not followed with all layers. For example, the Biophysical Permafrost Zones and Communities layers are visible when you open the demo portal, but both are set to false in the XML. If this issue persists after updating, open a new ticket for this in metacatui.

See example code for downloading the latest version of the portal in viz-info

Note that this issue is not related to the viz-workflow itself, but rather is generally a TODO item for the project.