[Task] Update Atlascope footprints output

[mradamcox]

Describe the task

The atlascope endpoint for footprints needs a few small updates. Example: https://oldinsurancemaps.net/atlascope/footprints/detroit-mi

• only include atlases that have a static xyz url available
• change structure of source to be this:

  source	
      type: "xyz"
      url: path to {z}/{x}/{y}.png"
  

• update bibliographic attributes as needed