Implement cv.gin and multiple output for python

modules/python/src2/cv2.cpp

@@ -1954,6 +1954,7 @@ static PyMethodDef special_methods[] = {
 #ifdef HAVE_OPENCV_GAPI
   {"GIn", CV_PY_FN_WITH_KW(pyopencv_cv_GIn), "GIn(...) -> GInputProtoArgs"},
   {"GOut", CV_PY_FN_WITH_KW(pyopencv_cv_GOut), "GOut(...) -> GOutputProtoArgs"},
+  {"gin", CV_PY_FN_WITH_KW(pyopencv_cv_gin), "gin(...) -> GRunArgs"},
 #endif
   {NULL, NULL},
 };