This task is to determine the list of fields to be indexed for an image file, i.e. page in NS_FILE namespace.
Proposed fields:
| media_type | keyword | file type |
| mime | keyword | file mime type |
| size | int | file size |
| width | int | Image width |
| height | int | Image height |
| resolution | int | floor(sqrt(width*height)) |
| bits | int | image bit depth |