schema can be modified by a service discovery provider

Author: nurhat

src/Ocelot/Configuration/DownstreamReRoute.cs

@@ -90,7 +90,7 @@ public DownstreamReRoute(
         public bool UseServiceDiscovery { get; }
         public bool EnableEndpointEndpointRateLimiting { get; }
         public QoSOptions QosOptions { get; }
-        public string DownstreamScheme { get; }
+        public string DownstreamScheme { get; set; }
         public string RequestIdKey { get; }
         public bool IsCached { get; }
         public CacheOptions CacheOptions { get; }