feat: preview server configuration and usage

[Zoramite]

Currently the editor does not correctly do previewing since the preview server has been separated from the UI. This work add the configuration ability for projects to have a preview server url and configuration.

Preview servers are required to return a config file that has the route information that the editor can map from the file path to the serving url:

For example:

{
  "routes": {
    "/content/pages/index.yaml": {
      "en": {
        "path": "/",
        "title": "Coolest site evar!",
      },
    "/static/images/foo.png": {
        "path": "/img/foo.png"
      }
    }
  }
}