Add IUTF8 terminal mode.

src/Renci.SshNet/Common/TerminalModes.cs

@@ -160,6 +160,11 @@
         /// </summary>
         IMAXBEL = 41,
 
+        /// <summary>
+        /// Terminal input and output is assumed to be encoded in UTF-8.
+        /// </summary>
+        IUTF8 = 42,
+
         /// <summary>
         /// Enable signals INTR, QUIT, [D]SUSP.
         /// </summary>