Bug: wrong x and y in lat_lon_to_closest_variable_indices and lat_lon_boundingbox_to_variable_indices

The longitude value is obtained by **x** coordinates whereas latitude by **y**:
```python
"longitude": bmi.get_grid_x(grid),
"latitude": bmi.get_grid_y(grid),
```

This is not the case in two functions implemented in util.py:
[lat_lon_to_closest_variable_indices](https://github.com/eWaterCycle/ewatercycle/blob/1156a4ff7cdc1fc7143d0cc1137695c405581f55/ewatercycle/util.py#L43)
[lat_lon_boundingbox_to_variable_indices](https://github.com/eWaterCycle/ewatercycle/blob/1156a4ff7cdc1fc7143d0cc1137695c405581f55/ewatercycle/util.py#L69)