rtaib

Backend default to Agg preventing plotting when testing styles programmatically

2

### Description When testing the styles programmatically in a Notebook, [as per the documentation](https://datacube-ows.readthedocs.io/en/latest/styling_howto.html#introduction-testing-styles:~:text=plot_image_with_style_cfg(rgb_cfg%2C%20data%2C%20x%3D%22longitude%22%2C%20y%3D%22latitude%22)) the plots do not show because the backend is set to `Agg` by `datacube_ows/styles/ramp.py`. The user...