Use the DOTNET_ env var prefix dotnet/extensions#4150 (dotnet/extensi…

…ons#1084)

Commit migrated from dotnet/extensions@40dc8fa

src/libraries/Microsoft.Extensions.Hosting/src/Host.cs

@@ -20,7 +20,7 @@ public static IHostBuilder CreateDefaultBuilder(string[] args)
             builder.UseContentRoot(Directory.GetCurrentDirectory());
             builder.ConfigureHostConfiguration(config =>
             {
-                config.AddEnvironmentVariables(); // TODO: Prefix?
+                config.AddEnvironmentVariables("DOTNET_");
                 if (args != null)
                 {
                     config.AddCommandLine(args);