FR: Option to use existing supplier parts when updating

[zenermerps]

When updating your database with --update or --update-recursive it would be great to add a extra flag to use the already existing supplier parts to pull new data, as I renamed the parts to something more human-readable than just the MPN, which breaks updating them, because the searches in the supplier APIs don't return any results with those readable names.

A possible way around this would be to tell inventree-part-import to disregard the name and use the information in the linked supplier and/or manufacturer parts to pull the new information for the currently updating part.