Support terminal resizing for exec/attach/run

Add support for terminal resizing for exec, attach, and run. Note that for Docker, exec sessions
inherit the environment from the primary process, so if the container was created with tty=false,
that means the exec session's TERM variable will default to "dumb". Users can override this by
setting TERM=xterm (or whatever is appropriate) to get the correct "smart" terminal behavior.

pkg/api/types.go

@@ -2751,6 +2751,8 @@ const (
 	StreamTypeData = "data"
 	// Value for streamType header for error stream
 	StreamTypeError = "error"
+	// Value for streamType header for terminal resize stream
+	StreamTypeResize = "resize"
 
 	// Name of header that specifies the port being forwarded
 	PortHeader = "port"