Describe the feature and motivation

It seems that OpenCV currently uses OpenEXR internally via a limited interface and strips away access to the underlying Imf::Header structure. Exposing a way to either:

• Pass custom metadata fields as an argument to cv::imwrite()
• Provide a lower-level cv::imwriteEXR(), allowing access to editing metadatas.

Modifying cv::imwrite would result in a massive PR. Instead, adding a separate method cv::imwriteEXR() could be a POC for now and other formats(..JPEG, JPEGXL,PNG.. ) could also benefit from this if it turns out to be a useful feature.