Add field for reference syncing in config file.

Contentless/Config.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Collections.Generic;
 using Newtonsoft.Json;
 
@@ -14,6 +15,8 @@ public class Config {
     [JsonProperty("overrides")]
     public Dictionary<string, Override> Overrides = new();
     
+    [JsonProperty("references")] 
+    public string[] References = Array.Empty<string>();
 }
 
 public class Override {

Test/Content/Contentless.json

@@ -5,6 +5,7 @@
         "Ex*.png"
     ],
     "logSkipped": false,
+    "references": ["monogame.extended.content.pipeline"],
     "overrides": {
         "Copy.*": {
             "copy": true