Add Brotli file compression

Author: mythz

src/ServiceStack.Text/HttpUtils.cs

@@ -2006,30 +2006,32 @@ public static class HttpMethods
 
     public static class CompressionTypes
     {
-        public static readonly string[] AllCompressionTypes = new[] { Deflate, GZip };
+        public static readonly string[] AllCompressionTypes = { Deflate, GZip };
 
         public const string Default = Deflate;
+        public const string Brotli = "br";
         public const string Deflate = "deflate";
         public const string GZip = "gzip";
 
         public static bool IsValid(string compressionType)
         {
-            return compressionType == Deflate || compressionType == GZip;
+            return compressionType is Deflate or GZip or Brotli;
         }
 
         public static void AssertIsValid(string compressionType)
         {
             if (!IsValid(compressionType))
             {
                 throw new NotSupportedException(compressionType
-                    + " is not a supported compression type. Valid types: gzip, deflate.");
+                    + " is not a supported compression type. Valid types: gzip, deflate, br.");
             }
         }
 
         public static string GetExtension(string compressionType)
         {
             switch (compressionType)
             {
+                case Brotli:
                 case Deflate:
                 case GZip:
                     return "." + compressionType;