Static files/directory config for appsettings.json

[xXBuilderBXx]

Add support for configuring static files/directories with appsettings.json just like how nginx allows it.

The key can be default Address or it could be named Path to seperate it.
Nginx also allows to specify an index file like index index.html; this could also be used as another value "Index": "index.html"

"ReverseProxy": {
    "Routes": [
      {
        "RouteId": "route1",
        "ClusterId": "cluster1",
        "Match": {
          "Path": "{**catch-all}"
        }
      }
    ],
    "Clusters": {
      "cluster1": {
        "Destinations": {
          "cluster1/destination1": {
            "Address": "/linux/path/here/"
          }
        }
      }
    }
  }

[Tratcher]

Duplicate of #187

This is tangential to YARP's primarily concern as a library for routing to external sources. We do consider static file config important in the pre-built exe scenario that would be comparable to nginx.

I don't envision this as being part of the cluster config, none of the cluster settings make sense for static assets. I expect it would use a different config section entirely.

[samsp-msft]

What is missing here (possibly more from ASP.NET than YARP) is a standard config section for configuring static files. In the same way that you add the config provider to YARP, it would nice to be able to specify a config section that would map to a StaticFileOptions instance enabling the configuration of folders, headers, auth, content types etc from config rather than code.

Not that difficult to write, but probably not a high priority for YARP v1.

[karelz]

Duplicate of #187