Allow URL to be an object

[andrewharvey]

As I realised in #2626 the ESRI service URLs can be quite complex, we should consider extending the schema so the URL can be provided as an object which would then be assembled by the build into the current output.

This makes it much easier for humans to create, review and modify the URL.

before

"url": "https://portal.spatial.nsw.gov.au/server/rest/services/StrataHub/MapServer/export?layers=show%3A0&imageSR={wkid}&bbox={bbox}&bboxSR={wkid}&format=png32&size={width},{height}&transparent=true&f=image&dynamicLayers=%5B%0D%0A%7B%0D%0A%22id%22%3A0%2C%0D%0A%22source%22%3A%7B%0D%0A%22type%22%3A%22mapLayer%22%2C%0D%0A%22mapLayerId%22%3A0%0D%0A%7D%2C%0D%0A%22drawingInfo%22%3A%7B%0D%0A%22renderer%22%3A%7B%0D%0A%22type%22%3A%22simple%22%2C%0D%0A%22symbol%22%3A%7B%0D%0A%22type%22%3A%22esriSFS%22%2C%0D%0A%22style%22%3A%22esriSFSSolid%22%2C%0D%0A%22color%22%3A%5B201%2C242%2C252%2C128%5D%2C%0D%0A%22outline%22%3A%7B%0D%0A%22type%22%3A%22esriSLS%22%2C%0D%0A%22style%22%3A%22esriSLSolid%22%2C%0D%0A%22color%22%3A%5B110%2C110%2C110%2C255%5D%2C%0D%0A%22width%22%3A1%0D%0A%7D%0D%0A%7D%0D%0A%7D%0D%0A%7D%0D%0A%7D%0D%0A%5D%0D%0A",

after

{
  url: "https://portal.spatial.nsw.gov.au/server/rest/services/StrataHub/MapServer/export",
  searchParams: {
    layers: "show:0",
    imageSR: "{wkid}",
    bbox: "{bbox}",
    bboxSR: "{wkid}",
    format: "png32",
    size: "{width},{height}",
    transparent: "true",
    f: "image",
    dynamicLayers: [
      {
        "id": 0,
        "source": {
          "type": "mapLayer",
          "mapLayerId": 0
        },
        "drawingInfo": {
          "renderer": {
            "type": "simple",
            "symbol": {
              "type": "esriSFS",
              "style": "esriSFSSolid",
              "color": [
                201,
                242,
                252,
                128
              ],
              "outline": {
                "type": "esriSLS",
                "style": "esriSLSolid",
                "color": [
                  110,
                  110,
                  110,
                  255
                ],
                "width": 0
              }
            }
          }
        }
      }
    ]
  }
}