Descripe the feature and motivation

I'd like to read my images with IMREAD_UNCHANGED so that the number of channels is automatically inferred from the image file, but I'd like the exif orientation to be applied. All other configurations are supported except this one:

• IMREAD_COLOR -> apply exif
• IMREAD_COLOR | IMREAD_IGNORE_ORIENTATION -> ignore exif
• IMREAD_UNCHANGED -> ignore exif

Additional context

I'd be glad to add a PR but I'm not sure what's the best solution to modify these flags.