[FEATURE REQUEST] remove duplicates while keeping external library image

[simulot]

Discussed in https://github.com/simulot/immich-go/discussions/75

^{Originally posted by traktuner November 13, 2023} Hello! I currently have the following issue: I imported many pictures into immich via cli some time ago which are present in photo album folders on my NAS drive. Not long ago, the external library feature was implemented which I am using a lot. So I have many duplicates now, because lots of albums I manually imported are now part of some external libraries. It would be really cool if you could add a routine (or separate deduplicate function) to check if assets in the user library match a file exactly which is present in an external library, and if yes - trash the uploaded picture (and update the albums with the "new" file instead) When I do that now, it would like to remove the one from the external library but of cours that is a read only volume. Hope that makes sense!

Thank you very much for that useful project!