immich-app/immich#16062 added manual face tagging and deletion, but did
not add a new 'SourceType'. The create faces would default to
'machine-learning' which is incorrect, and has the annoying downside
that they will be wiped when the 'Refresh Faces' job is run.
Handling of non-machine-learning faces was previously added in
immich-app/immich#6455. This PR simply extends it to the new manually
tagged faces.