Organizations: allow uploading avatar (#12254)
- The file size is set to 750kb as max
- The image dimensions should be equal or less to 500px
- Only jpg and png formats are allowed (this is a soft check anyway), we
are not checking for the content, but django does check if the file is
an image using pillow at least.
- Images are publicly accessible and can be enumerated, I think this is
fine, avatar images aren't sensible information.
- pillow is a required dependency when using ImageField
This requires creating a new bucket and the corresponding settings in
ops.
Closes https://github.com/readthedocs/readthedocs-corporate/issues/1471
