Copy lens correction metadata into merged HDR files

Is your feature request related to a problem? Please describe.
I'm using a DJI Mini 3 which outputs raw DNG files with lens correction metadata in them, which is recognized and used by the "Lens correction" module in darktable (as of #12880). However, when a set of exposure-bracketed images is merged via "Create HDR", that part of the metadata is lost and lens correction does not work on the resulting HDR image.

Describe the solution you'd like
Lens correction metadata should be copied over into HDR merged images, like other EXIF tags are currently copied over.

Alternatives
In my specific case, I've found that manually applying the TCA & vignetting corrections from the Huawei P30 Pro entry in the lens database works just as well as the embedded metadata. I understand there are also external preprocessors that can apply lens corrections to individual shots before merging, but I haven't tried that.

Additional context
A sample set of 3 bracketed shots with lens correction metadata:
https://www.dropbox.com/s/6kmzy3ntkejrogp/sample_aeb_hdr_lens_correction.zip?dl=0

Start by locating the HDR merge handling and the existing EXIF-tag copying path in darktable. Use the linked bracketed sample set to verify the behavior; done means lens correction metadata is retained in the merged HDR output and the Lens correction module can use it.