Is there a way to convert/move external library assets to be internal?

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Basically I started from scratch and mounted my past library of photos as an external library to test out Immich. I'm now pretty happy with it and it'd be nice to get all the files (old and newly uploaded from my phone) under the same folder structure, but I don't want to have to perform all the indexing/generating/detecting again. So how can I move that stuff?