[Feature] Initially read and eventually write face metadata

The feature It seems like the original discussion around face metadata was closed so opening up a separate request here. It would be great for Immich to be able to read existing face metadata from pictures (or XMP files). Examples of other software which read face metadata include PiGallery2 and Digikam. At worst case this data could be used as "hints" to Immich's face recognition system where if there was a significant overlap with and existing face region and an Immich discovered face region Immich might assume the existing metadata to be correct and suggest or even automatically tag that region in Immich's database. At best case Immich could use/display the actual face regions from either photos metadata or from accompanying XMP sidecar files. Secondarily, it would be nice if Immich could write face metadata that was created/modified using Immich in a fashion which could be re-used by other photo management software. An example of an existing software…