Implemented "location" option for "return" action.

This allows to specify redirects:

  {
      "action": {
          "return": 301,
          "location": "https://www.example.com/"
      }
  }

src/nxt_h1proto.c

@@ -1103,6 +1103,8 @@ static const nxt_str_t  nxt_http_redirection[] = {
     nxt_string("HTTP/1.1 302 Found\r\n"),
     nxt_string("HTTP/1.1 303 See Other\r\n"),
     nxt_string("HTTP/1.1 304 Not Modified\r\n"),
+    nxt_string("HTTP/1.1 307 Temporary Redirect\r\n"),
+    nxt_string("HTTP/1.1 308 Permanent Redirect\r\n"),
 };